TWI878392B - Flexible signaling of qp offset for adaptive color transform in video coding - Google Patents

Abstract

A video decoder can be configured to determine that a block of the video data is encoded using an adaptive color transform (ACT); determine that the block is encoded in a joint chroma mode, wherein for the joint chroma mode a single chroma residual block is encoded for a first chroma component of the block and a second chroma component of the block; determine a quantization parameter (QP) for the block; determine an ACT quantization parameter (QP) offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode; and determine an ACT QP for the block based on the QP and the ACT QP offset.

Description

Flexible signaling of QP offsets for self-adjusting color transitions in video coding

This application claims the benefit of U.S. Provisional Patent Application No. 62/940,728 filed on November 26, 2019, and U.S. Provisional Patent Application No. 62/954,318 filed on December 27, 2019, both of which are hereby incorporated by reference in their entirety.

This disclosure relates to video encoding and video decoding.

Digital video capabilities can be incorporated into a wide variety of devices, including digital televisions, digital live broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radios (so-called "smart phones"), video teleconferencing equipment, video streaming devices, and many others. Digital video devices implement video coding techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4 (Part 10, Advanced Video Coding (AVC)), ITU-T H.265/High Efficiency Video Coding (HEVC), and extensions of such standards. By implementing such video coding techniques, video devices can more efficiently send, receive, encode, decode and/or store digital video information.

Video coding techniques include spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) can be partitioned into video blocks, which can also be referred to as coding tree units (CTUs), coding units (CUs), and/or coding nodes. Video blocks in an intra-frame coded (I) slice of a picture are coded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-frame coded (P or B) slice of a picture can use spatial prediction relative to reference samples in neighboring blocks in the same picture or temporal prediction relative to reference samples in other reference pictures. A picture may be referred to as a frame, and a reference picture may be referred to as a reference frame.

The present disclosure describes techniques for encoding blocks of video data using both an adaptive color transform (ACT) and a joint chroma mode that can provide improved coding efficiency compared to prior art techniques for using ACT in conjunction with a joint chroma mode. As will be explained in more detail below, when using ACT, a video encoder and a video decoder apply an offset to a quantization parameter (QP) value to determine an ACT QP value. The video encoder and the video decoder then use the ACT QP value to quantize and dequantize transform coefficients. The present disclosure describes techniques for determining an ACT QP offset that can improve overall video coding efficiency for coding scenes that use ACT in conjunction with a joint chroma mode. More specifically, by determining an ACT QP offset for a block based on whether the block is encoded using ACT and is encoded in joint chroma mode, and determining an ACT QP for the block based on the QP and the ACT QP offset, the techniques of the present disclosure can improve the overall encoding quality of video data in encoding scenarios using both ACT and joint chroma mode.

According to one example, a method for decoding video data includes: determining that a block of the video data is encoded using an adaptive color transform (ACT); determining that the block is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for a first chroma component of the block and a second chroma component of the block; determining a quantization parameter (QP) for the block; determining an ACT quantization parameter (QP) offset for the block based on that the block is encoded using the ACT and is encoded in the joint chroma mode; determining an ACT QP for the block based on the QP and the ACT QP offset; determining an ACT QP for the block based on the ACT The invention relates to a method for determining a single chroma residue block based on a QP; determining a first chroma residue block for the first chroma component according to the single chroma residue block, wherein the first chroma residue block is in a first color space; determining a second chroma residue block for the second chroma component according to the single chroma residue block, wherein the second chroma residue block is in the first color space; performing an inverse ACT on the first chroma residue block to convert the first chroma residue block to a second color space; and performing the inverse ACT on the second chroma residue block to convert the second chroma residue block to the second color space.

According to one example, a device for decoding video data includes a memory configured to store the video data and one or more processors, the one or more processors being implemented in circuitry and configured to: determine that a block of the video data is encoded using an adaptive color transform (ACT); determine that the block is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for a first chroma component of the block and a second chroma component of the block; determine a quantization parameter (QP) for the block; determine an ACT quantization parameter (QP) offset for the block based on the block being encoded using the ACT and being encoded in the joint chroma mode; and determine a QP offset based on the QP and the ACT. QP offset to determine the ACT QP for the block; based on the ACT QP for the block The invention relates to a method for determining a single chroma residue block based on a QP; determining a first chroma residue block for the first chroma component according to the single chroma residue block, wherein the first chroma residue block is in a first color space; determining a second chroma residue block for the second chroma component according to the single chroma residue block, wherein the second chroma residue block is in the first color space; performing an inverse ACT on the first chroma residue block to convert the first chroma residue block to a second color space; and performing the inverse ACT on the second chroma residue block to convert the second chroma residue block to the second color space.

According to another example, an apparatus for decoding video data includes: means for determining that a block of the video data is encoded using an adaptive color transform (ACT); means for determining that the block is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for a first chroma component of the block and a second chroma component of the block; means for determining a quantization parameter (QP) for the block; means for determining an ACT quantization parameter (QP) offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode; means for determining an ACT QP offset for the block based on the QP and the ACT QP offset. QP component; used based on the ACT used for the block A component for determining the single chroma residue block based on a QP; a component for determining a first chroma residue block for the first chroma component based on the single chroma residue block, wherein the first chroma residue block is in a first color space; a component for determining a second chroma residue block for the second chroma component based on the single chroma residue block, wherein the second chroma residue block is in the first color space; a component for performing an inverse ACT on the first chroma residue block to convert the first chroma residue block to a second color space; and a component for performing the inverse ACT on the second chroma residue block to convert the second chroma residue block to the second color space.

According to another example, a computer-readable storage medium stores instructions that, when executed by one or more processors, cause the one or more processors to perform the following operations: determine that a block of video data is encoded using an adaptive color transform (ACT); determine that the block is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for a first chroma component of the block and a second chroma component of the block; determine a quantization parameter (QP) for the block; determine an ACT quantization parameter (QP) offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode; determine an ACT QP offset for the block based on the QP and the ACT QP offset. QP; determining the single chroma residue block based on the ACT QP for the block; determining a first chroma residue block for the first chroma component based on the single chroma residue block, wherein the first chroma residue block is in a first color space; determining a second chroma residue block for the second chroma component based on the single chroma residue block, wherein the second chroma residue block is in the first color space; performing an inverse ACT on the first chroma residue block to convert the first chroma residue block to a second color space; and performing the inverse ACT on the second chroma residue block to convert the second chroma residue block to the second color space.

According to another example, a method for encoding video data includes: determining a first chroma residue block for a first chroma component of a block of video data; determining a second chroma residue block for a second chroma component of the block of video data, wherein the first chroma residue block and the second chroma residue block are in a first color space; determining that the block of video data is encoded using an adaptive color transform (ACT); performing the ACT on the first chroma residue block to convert the first chroma residue block to a second color space; performing an inverse ACT on the second chroma residue block to convert the second chroma residue block to a second color space; The method comprises: converting a block of the video data to the second color space; determining that the block of the video data is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for the first chroma component of the block and the second chroma component of the block; determining the single chroma residue block based on the converted first chroma residue block and the converted second chroma residue block; determining a quantization parameter (QP) for the block; determining an ACT quantization parameter (QP) offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode; determining a QP offset for the block based on the QP and the ACT The method further comprises: determining an ACT QP for the block using the QP offset; and quantizing the single chroma residue block based on the ACT QP for the block.

According to another example, a device for encoding video data includes a memory configured to store the video data and one or more processors, the one or more processors being implemented in circuitry and configured to: determine a first chroma residue block for a first chroma component of a block of video data; determine a second chroma residue block for a second chroma component of the block of video data, wherein the first chroma residue block and the second chroma residue block are in a first color space; determine that the block of video data is encoded using an adaptive color transform (ACT); perform the ACT on the first chroma residue block to convert the first chroma residue block to a second color space; and perform the ACT on the second chroma residue block to convert the first chroma residue block to a second color space. The method comprises performing an inverse ACT on a chroma residue block to convert the second chroma residue block to the second color space; determining that the block of the video data is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for the first chroma component of the block and the second chroma component of the block; determining the single chroma residue block based on the converted first chroma residue block and the converted second chroma residue block; determining a quantization parameter (QP) for the block; determining an ACT quantization parameter (QP) offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode; and determining a QP offset based on the QP and the ACT. The method further comprises: determining an ACT QP for the block using the QP offset; and quantizing the single chroma residue block based on the ACT QP for the block.

According to another example, an apparatus for encoding video data includes: means for determining a first chroma residue block for a first chroma component of a block of video data; means for determining a second chroma residue block for a second chroma component of the block of video data, wherein the first chroma residue block and the second chroma residue block are in a first color space; means for determining that the block of video data is encoded using an adaptive color transform (ACT); means for performing the ACT on the first chroma residue block to convert the first chroma residue block to a second color space; means for performing an inverse ACT on the second chroma residue block to convert the second chroma residue block to a second color space; means for determining that the block of video data is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for the first chroma component of the block and the second chroma component of the block; means for determining the single chroma residue block based on the converted first chroma residue block and the converted second chroma residue block; means for determining a quantization parameter (QP) for the block; means for determining an ACT quantization parameter (QP) offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode; means for determining an ACT quantization parameter (QP) offset for the block based on the QP and the ACT means for determining an ACT QP for the block based on a QP offset; and means for quantizing the single chroma residue block based on the ACT QP for the block.

According to another example, a computer-readable storage medium stores instructions that, when executed by one or more processors, cause the one or more processors to: determine a first chroma residue block for a first chroma component of a block of video data; determine a second chroma residue block for a second chroma component of the block of video data, wherein the first chroma residue block and the second chroma residue block are in a first color space; determine that the block of video data is encoded using an adaptive color transform (ACT); perform the ACT on the first chroma residue block to convert the first chroma residue block to a second color space; perform the ACT on the second chroma residue block; The method comprises performing an inverse ACT to convert the second chroma residue block to the second color space; determining that the block of the video data is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for the first chroma component of the block and the second chroma component of the block; determining the single chroma residue block based on the converted first chroma residue block and the converted second chroma residue block; determining a quantization parameter (QP) for the block; determining an ACT quantization parameter (QP) offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode; and determining a QP offset for the block based on the QP and the ACT. The method further comprises: determining an ACT QP for the block using the QP offset; and quantizing the single chroma residue block based on the ACT QP for the block.

The details of one or more embodiments of the present disclosure are set forth in the accompanying drawings and the following description. Other features, objectives, and advantages of the present disclosure will be apparent from the description, drawings, and claims.

Video coding (e.g., video encoding and/or video decoding) typically involves predicting a block of video data from an already coded block of video data in the same picture (e.g., intra-frame prediction) or predicting a block of video data from an already coded block of video data in a different picture (e.g., inter-frame prediction). In some cases, the video coder also computes residual data by comparing the predicted block to the original block. Thus, the residual data represents the difference between the predicted block and the original block. To reduce the number of bits required to signal the residue data, the video encoder transforms and quantizes the residue data, and signals the transformed and quantized residue data in the encoded bit stream. The compression achieved by the transform and quantization process may be lossy, meaning that the transform and quantization process may introduce distortion into the decoded video data. The amount of quantization is controlled by a quantization parameter (QP). In some cases, the video encoder may also apply an adaptive color transform (ACT) to the residue data prior to the transform and quantization to convert the residue data from a first color space to a second color space. For example, ACT may be used in encoding scenarios where the residue data may be more efficiently encoded in the second color space than in the first color space.

The video decoder performs inverse quantization, inverse transform, and inverse ACT to decode the residual data, and then adds the decoded residual data to the prediction block to produce a reconstructed video block that more closely matches the original video block (compared to the prediction block alone). The first reconstructed block may have distortion or artifacts due to the loss introduced by the transform and quantization of the residual data. One common type of artifact or distortion is called blocking, where the boundaries of the blocks used to encode the video data are visible.

To further improve the quality of the decoded video, the video decoder may perform one or more filtering operations on the reconstructed video blocks. Examples of such filtering operations include deblocking filtering, sample self-adjusted offset (SAO) filtering, and self-adjusting loop filtering (ALF). Parameters for such filtering operations may be determined by the video encoder and explicitly signaled in the coded video bit stream, or may be implicitly determined by the video decoder without explicitly signaling such parameters in the coded video bit stream.

As will be explained in more detail below, video data is often encoded as a block of luma samples and two corresponding blocks of chroma samples. Video data can be encoded in a joint-chroma mode (also called joint-CbCr mode), in which the video encoder encodes a single chroma residue block for two corresponding blocks of chroma residue samples, and then the video decoder derives the two corresponding blocks of chroma residue samples from the single chroma residue block.

The present disclosure describes techniques for encoding blocks of video data using both ACT and a joint chroma mode (e.g., a joint CbCr mode) that can provide improved coding efficiency compared to prior art techniques for using ACT in conjunction with a joint chroma mode. As will be explained in more detail below, when using ACT, a video encoder and a video decoder apply an offset to a QP value to determine an ACT QP value. The video encoder and the video decoder then use the ACT QP value to quantize and dequantize transform coefficients. The present disclosure describes techniques for determining an improved ACT QP offset that can improve overall video coding efficiency for coding scenes that use ACT in conjunction with a joint chroma mode. More specifically, by determining an ACT QP offset for a block based on whether the block is encoded using ACT and is encoded in joint chroma mode, and determining an ACT QP for the block based on the QP and the ACT QP offset, the techniques of the present disclosure can improve the overall encoding quality of video data in encoding scenarios using both ACT and joint chroma mode.

FIG. 1 is a block diagram illustrating an example video encoding and decoding system 100 in which the techniques of the present disclosure may be implemented. In general, the techniques of the present disclosure relate to encoding (encoding and/or decoding) video data. In general, video data includes any data used to process video. Thus, video data may include original unencoded video, encoded video, decoded (e.g., reconstructed) video, and video relay data (e.g., signaling data).

1 , in this example, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. Specifically, source device 102 provides the video data to destination device 116 via computer-readable medium 110. Source device 102 and destination device 116 may include any of a wide variety of devices, including desktop computers, notebook computers (i.e., laptops), mobile devices, tablet computers, set-top boxes, mobile phones (e.g., smart phones), televisions, cameras, display devices, digital media players, video game consoles, video data streaming devices, broadcast receiver devices, etc. In some cases, source device 102 and destination device 116 may be equipped for wireless communications and, therefore, may be referred to as wireless communication devices.

In the example of FIG. 1 , source device 102 includes video source 104, memory 106, video encoder 200, and output interface 108. Destination device 116 includes input interface 122, video decoder 300, memory 120, and display device 118. According to the present disclosure, video encoder 200 of source device 102 and video decoder 300 of destination device 116 can be configured to apply techniques for flexible signaling for QP offset for ACT. Thus, source device 102 represents an instance of a video encoding device, and destination device 116 represents an instance of a video decoding device. In other examples, source device and destination device may include other components or arrangements. For example, source device 102 may receive video data from an external video source such as an external camera. Likewise, destination device 116 may interface with an external display device rather than including an integrated display device.

The system 100 shown in FIG. 1 is merely an example. In general, any digital video encoding and/or decoding device may implement techniques for flexible signaling of QP offsets for ACTs. Source device 102 and destination device 116 are merely examples of such encoding devices, where source device 102 generates encoded video data for transmission to destination device 116. The present disclosure represents a "coding" device as a device that performs encoding (e.g., encoding and/or decoding) of data. Thus, video encoder 200 and video decoder 300 represent examples of encoding devices, specifically, a video encoder and a video decoder, respectively. In some examples, source device 102 and destination device 116 can operate in a substantially symmetrical manner such that each of source device 102 and destination device 116 includes video encoding and decoding components. Thus, system 100 can support one-way or two-way video transmission between source device 102 and destination device 116, for example, for video data streaming, video playback, video broadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e., raw, unencoded video data) and provides a sequential series of pictures (also referred to as "frames") of the video data to video encoder 200, which encodes the data for the pictures. Video source 104 of source device 102 may include a video capture device, such as a video camera, a video archive unit containing previously captured raw video, and/or a video feed interface for receiving video from a video content provider. As a further alternative, video source 104 may generate computer graphics-based data as source video, or a combination of real-time video, archived video, and computer-generated video. In each case, the video encoder 200 can encode captured, pre-captured, or computer-generated video data. The video encoder 200 can rearrange the pictures from the order in which they were received (sometimes referred to as "display order") to a coding order for encoding. The video encoder 200 can generate a bit stream including the encoded video data. The source device 102 can then output the encoded video data to the computer-readable medium 110 via the output interface 108 to be received and/or retrieved by, for example, the input interface 122 of the destination device 116.

The memory 106 of the source device 102 and the memory 120 of the destination device 116 represent general purpose memories. In some examples, the memories 106, 120 can store raw video data, such as raw video from the video source 104 and raw decoded video data from the video decoder 300. Additionally or alternatively, the memories 106, 120 can store software instructions that can be executed by, for example, the video encoder 200 and the video decoder 300, respectively. Although the memory 106 and the memory 120 are shown in this example as being separate from the video encoder 200 and the video decoder 300, it should be understood that the video encoder 200 and the video decoder 300 may also include internal memory for functionally similar or equivalent purposes. In addition, the memory 106, 120 may store, for example, encoded video data output from the video encoder 200 and input to the video decoder 300. In some examples, portions of the memory 106, 120 may be allocated as one or more video buffers, for example, to store raw decoded and/or encoded video data.

Computer-readable medium 110 may represent any type of medium or device capable of transmitting encoded video data from source device 102 to destination device 116. In one example, computer-readable medium 110 represents a communication medium that enables source device 102 to send encoded video data directly to destination device 116 in real time, such as via a radio frequency network or a computer-based network. Output interface 108 may modulate a transmission signal including the encoded video data according to a communication standard such as a wireless communication protocol, and input interface 122 may demodulate a received transmission signal according to a communication standard such as a wireless communication protocol. The communication medium may include any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other device that may be useful for facilitating communication from the source device 102 to the destination device 116.

In some examples, source device 102 can output the encoded data from output interface 108 to storage device 112. Similarly, destination device 116 can access the encoded data from storage device 112 via input interface 122. Storage device 112 can include any of a variety of distributed or locally accessed data storage media, such as a hard drive, Blu-ray Disc, DVD, CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output the encoded video data to file server 114 or another intermediate storage device that may store the encoded video data generated by source device 102. Destination device 116 may access the stored video data from file server 114 via data streaming or downloading.

The file server 114 may be any type of server device capable of storing encoded video data and sending the encoded video data to the destination device 116. The file server 114 may represent a web server (e.g., for a website), a server configured to provide file transfer protocol services (such as the File Transfer Protocol (FTP) or the File Delivery over One-Way Transport (FLUTE) protocol), a content delivery network (CDN) device, a Hypertext Transfer Protocol (HTTP) server, a Multimedia Broadcast Multicast Service (MBMS) or an enhanced MBMS (eMBMS) server, and/or a Network Attached Storage (NAS) device. The file server 114 may additionally or alternatively implement one or more HTTP data streaming protocols, such as Dynamic Self-Adjusting Data Streaming over HTTP (DASH), HTTP Live Streaming (HLS), Real-Time Streaming Protocol (RTSP), HTTP Dynamic Data Streaming, etc.

The destination device 116 may access the encoded video data from the file server 114 through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., digital subscriber line (DSL), cable modem, etc.), or a combination of the two suitable for accessing the encoded video data stored on the file server 114. The input interface 122 may be configured to operate according to any one or more of the various protocols discussed above for retrieving or receiving media data from the file server 114, or other such protocols for retrieving media data.

The output interface 108 and the input interface 122 may represent wireless transmitters/receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components operating in accordance with any of the various IEEE 802.11 standards, or other physical components. In instances where the output interface 108 and the input interface 122 include wireless components, the output interface 108 and the input interface 122 may be configured to transmit data (e.g., encoded video data) in accordance with a cellular communication standard (e.g., 4G, 4G-LTE (Long Term Evolution), Advanced LTE, 5G, etc.). In some examples where the output interface 108 includes a wireless transmitter, the output interface 108 and the input interface 122 may be configured to transmit data (e.g., encoded video data) in accordance with other wireless standards, such as the IEEE 802.11 specification, the IEEE 802.15 specification (e.g., ZigBee™), the Bluetooth™ standard, etc. In some examples, the source device 102 and/or the destination device 116 may include corresponding system-on-chip (SoC) devices. For example, the source device 102 may include a SoC device for performing the functions assigned to the video encoder 200 and/or the output interface 108, and the destination device 116 may include a SoC device for performing the functions assigned to the video decoder 300 and/or the input interface 122.

The techniques disclosed herein may be applied to video encoding to support any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, Internet streaming video transmission (such as Dynamic Self-Adapting Streaming over HTTP (DASH)), digital video encoded onto data storage media, decoding of digital video stored on data storage media, or other applications.

The input interface 122 of the destination device 116 receives the encoded video bit stream from the computer-readable medium 110 (e.g., communication media, storage device 112, file server 114, etc.). The encoded video bit stream may include signaling information such as the following syntax elements defined by the video encoder 200 (which are also used by the video decoder 300): The syntax elements have values that describe the characteristics and/or processing of video blocks or other coding units (e.g., slices, pictures, groups of pictures, sequences, etc.). The display device 118 displays the decoded pictures of the decoded video data to the user. Display device 118 may represent any of a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

Although not shown in FIG. 1 , in some examples, the video encoder 200 and the video decoder 300 may each be integrated with an audio encoder and/or an audio decoder and may include an appropriate MUX-DEMUX unit or other hardware and/or software to process multiplexed streams including both audio and video in a common data stream. If applicable, the MUX-DEMUX unit may comply with the ITU H.223 multiplexer protocol or other protocols such as the User Data Packet Protocol (UDP).

The video encoder 200 and the video decoder 300 can each be implemented as any of a variety of suitable encoder and/or decoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), individual logic, software, hardware, firmware, or any combination thereof. When the techniques are partially implemented in software, the device can store instructions for the software in a suitable non-transitory computer-readable medium and use one or more processors to execute the instructions in hardware to perform the techniques of the present disclosure. Each of the video encoder 200 and the video decoder 300 may be included in one or more coders or decoders, either of which may be integrated as part of a combined coder/decoder (CODEC) in a corresponding device. A device including the video encoder 200 and/or the video decoder 300 may include an integrated circuit, a microprocessor, and/or a wireless communication device (such as a cellular phone).

The video encoder 200 and the video decoder 300 may operate according to a video coding standard such as ITU-T H.265 (also known as High Efficiency Video Coding (HEVC)) or an extension thereof such as multi-view and/or scalable video coding extensions. Alternatively, the video encoder 200 and the video decoder 300 may operate according to other proprietary or industry standards such as ITU-T H.266, also known as Versatile Video Coding (VVC). The draft of the VVC standard is described in Bross et al., “Versatile Video Coding (Draft 7)”, Joint Video Experts Group (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 16th Meeting, Geneva, Switzerland, October 1-11, 2019, JVET-P2001-v14 (hereinafter referred to as “VVC Draft 7”). Another draft of the VVC standard is described in Bross et al., “Versatile Video Coding (Draft 10)”, Joint Video Experts Group (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 18th meeting by teleconference, June 22-July 1, 2020, JVET-S2001-v17 (hereinafter referred to as “VVC Draft 10”). However, the techniques of the present disclosure are not limited to any particular coding standard.

Typically, the video encoder 200 and the video decoder 300 can perform block-based encoding of a picture. The term "block" generally refers to a structure that includes data to be processed (e.g., to be encoded, decoded, or otherwise used in an encoding and/or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and/or chrominance data. Typically, the video encoder 200 and the video decoder 300 can encode video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, instead of encoding sampled red, green, and blue (RGB) data for a picture, the video encoder 200 and the video decoder 300 can encode luminance and chrominance components, where the chrominance components can include both red hue and blue hue chrominance components. In some examples, the video encoder 200 converts the received RGB formatted data into a YUV representation before encoding, and the video decoder 300 converts the YUV representation into an RGB format. Alternatively, a pre-processing and post-processing unit (not shown) may perform the conversions.

In general, the present disclosure may relate to the encoding of a picture (e.g., encoding and decoding) to include the process of encoding or decoding data for a picture. Similarly, the present disclosure may relate to the encoding of blocks of a picture to include the process of encoding or decoding data for the blocks (e.g., prediction and/or residual coding). The encoded video bit stream typically includes a series of values for syntax elements that represent coding decisions (e.g., coding modes) and the partitioning of the picture into blocks. Therefore, references to encoding a picture or block should generally be understood as encoding the values of the syntax elements used to form the picture or block.

HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video coding device (coder) (such as the video coder 200) divides a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video coding device divides the CTU and the CU into four equal, non-overlapping squares, and each node of the quadtree has zero or four child nodes. A node without child nodes may be referred to as a "leaf node", and the CU of such a leaf node may include one or more PUs and/or one or more TUs. The video coding device may further divide the PUs and TUs. For example, in HEVC, a residual quadtree (RQT) represents the partitioning of a TU. In HEVC, PU represents inter-frame prediction data, and TU represents residual data. An intra-frame predicted CU includes intra-frame prediction information, such as intra-frame mode indication.

As another example, the video encoder 200 and the video decoder 300 may be configured to operate according to VVC. According to VVC, a video encoding device (such as the video encoder 200) partitions a picture into a plurality of coding tree units (CTUs). The video encoder 200 may partition the CTU according to a tree structure (such as a quadtree-binary tree (QTBT) structure or a multi-type tree (MTT) structure). The QTBT structure removes the concept of multiple partition types, such as the separation between CU, PU, and TU of HEVC. The QTBT structure includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned according to binary tree partitioning. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of the binary tree correspond to the coding units (CUs).

In the MTT partitioning structure, blocks can be partitioned using quadtree (QT) partitioning, binary tree (BT) partitioning, and one or more types of ternary tree (TT) (also known as ternary tree (TT)) partitioning. Trinary tree or ternary tree partitioning is a partitioning in which a block is divided into three sub-blocks. In some examples, the ternary tree or ternary tree partitioning divides the block into three sub-blocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

In some examples, the video encoder 200 and the video decoder 300 may use a single QTBT or MTT structure to represent each of the luma component and the chroma components, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT/MTT structure for the luma component and another QTBT/MTT structure for the two chroma components (or two QTBT/MTT structures for the corresponding chroma components).

The video encoder 200 and the video decoder 300 may be configured to use quadtree partitioning, QTBT partitioning, MTT partitioning, or other partitioning structures per HEVC. For purposes of explanation, a description of the techniques of the present disclosure is provided with respect to QTBT partitioning. However, it should be understood that the techniques of the present disclosure may also be applied to video encoding devices configured to use quadtree partitioning or other types of partitioning.

In some examples, a CTU includes a coding tree block (CTB) of luma samples, two corresponding CTBs of chroma samples for a picture with three sample arrays, or a CTB of samples for a monochrome picture or a picture encoded using three separate color planes and a syntax structure for encoding the samples. A CTB can be an NxN block of samples (for some value of N) such that the division of components into CTBs is a partitioning. A component is an array or a single sample from one of the three arrays (one luma and two chroma) that make up a picture in 4:2:0, 4:2:2, or 4:4:4 color format, or an array or a single sample of an array that makes up a picture in monochrome format. In some examples, a coding block is an MxN block of samples (for some values of M and N), so that dividing the CTB into coding blocks is a partitioning.

Blocks (e.g., CTUs or CUs) can be grouped in a picture in various ways. As an example, a tile can represent a rectangular area of a CTU row within a particular tile in a picture. A tile can be a rectangular area of a CTU within a particular tile column and a particular tile row in a picture. A tile column represents a rectangular area of a CTU with a height equal to the height of the picture and a width specified by a syntax element (e.g., such as in a picture parameter set). A tile row represents a rectangular area of a CTU with a height specified by a syntax element (e.g., such as in a picture parameter set) and a width equal to the width of the picture.

In some examples, a tile may be partitioned into multiple bricks, each of which may include one or more CTU rows within the tile. Tiles that are not partitioned into multiple bricks may also be referred to as bricks. However, bricks that are true subsets of tiles may not be referred to as tiles.

The tiles in a picture can also be arranged in slices. A slice can be an integer number of tiles of a picture that can be uniquely contained in a single Network Abstraction Layer (NAL) unit. In some examples, a slice includes multiple complete tiles or a contiguous sequence of complete tiles of just one tile.

The present disclosure may use "NxN" and "N times N" interchangeably to represent the sample size of a block (such as a CU or other video block) in the vertical and horizontal dimensions, for example, 16x16 samples or 16 times 16 samples. Typically, a 16x16 CU will have 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). Similarly, an NxN CU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. The samples in a CU can be arranged in rows and columns. In addition, a CU does not necessarily need to have the same number of samples in the horizontal direction as in the vertical direction. For example, a CU may include NxM samples, where M is not necessarily equal to N.

The video encoder 200 encodes video data representing prediction and/or residual information and other information for a CU. The prediction information indicates how the CU will be predicted in order to form a prediction block for the CU. The residual information typically represents the sample-by-sample difference between the samples of the CU before encoding and the prediction block.

To predict a CU, the video encoder 200 may typically form a prediction block for the CU via inter-frame prediction or intra-frame prediction. Inter-frame prediction typically means predicting the CU based on data from a previously encoded picture, while intra-frame prediction typically means predicting the CU based on previously encoded data from the same picture. To perform inter-frame prediction, the video encoder 200 may use one or more motion vectors to generate the prediction block. The video encoder 200 may typically perform a motion search to identify a reference block that closely matches the CU, for example, in terms of the difference between the CU and the reference block. The video encoder 200 may calculate a difference metric using the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean square difference (MSD), or other such difference calculations to determine whether the reference block closely matches the current CU. In some examples, the video encoder 200 may predict the current CU using unidirectional prediction or bidirectional prediction.

Some implementations of VVC also provide an affine motion compensation mode, which can be considered an inter-frame prediction mode. In the affine motion compensation mode, the video encoder 200 can determine two or more motion vectors representing non-translational motion (such as zooming in or out, rotation, perspective motion, or other irregular motion types).

To perform intra-frame prediction, the video encoder 200 can select an intra-frame prediction mode to generate a prediction block. Some examples of VVC provide sixty-seven intra-frame prediction modes, including various directional modes, as well as planar modes and DC modes. Typically, the video encoder 200 selects an intra-frame prediction mode that describes the adjacent samples of the current block according to which the samples of the current block (e.g., a block of CU) are to be predicted. Assuming that the video encoder 200 encodes CTUs and CUs in raster scan order (from left to right, from top to bottom), such samples can typically be above, above left, or to the left of the current block in the same picture as the current block.

The video encoder 200 encodes data indicating a prediction mode for the current block. For example, for an inter-frame prediction mode, the video encoder 200 may encode data indicating which of various available inter-frame prediction modes to use and motion information for the corresponding mode. For unidirectional or bidirectional inter-frame prediction, for example, the video encoder 200 may encode motion vectors using advanced motion vector prediction (AMVP) or merge mode. The video encoder 200 may use a similar mode to encode motion vectors for an affine motion compensation mode.

After a prediction, such as intra-frame prediction or inter-frame prediction for a block, the video encoder 200 may calculate the residual data for the block. The residual data, such as a residual block, represents the sample-by-sample difference between the block and a predicted block for the block, which is formed using a corresponding prediction mode. The video encoder 200 may apply one or more transforms to the residual block to produce transformed data in a transform domain rather than in a sample domain. For example, the video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. Additionally, the video encoder 200 may apply a secondary transform after the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), etc. The video encoder 200 generates transform coefficients after applying one or more transforms.

As previously described, after any transformation to produce transform coefficients, the video encoder 200 may perform quantization of the transform coefficients. Quantization generally refers to a process in which the transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, thereby providing further compression. By performing the quantization process, the video encoder 200 may reduce the bit depth associated with some or all transform coefficients. For example, the video encoder 200 may round down an n -bit value to an m -bit value during quantization, where n is greater than m . In some examples, to perform quantization, the video encoder 200 may perform a bitwise right shift of the value to be quantized.

After quantization, the video encoder 200 can scan the transform coefficients to generate a one-dimensional vector from a two-dimensional matrix including the quantized transform coefficients. The scan can be designed to place the transform coefficients of higher energy (and therefore lower frequency) at the front of the vector and the transform coefficients of lower energy (and therefore higher frequency) at the back of the vector. In some examples, the video encoder 200 can scan the quantized transform coefficients using a predefined scan order to generate a serialized vector, and then entropy encode the quantized transform coefficients of the vector. In other examples, the video encoder 200 can perform self-adjusting scanning. After scanning the quantized transform coefficients to form a one-dimensional vector, the video encoder 200 may entropy encode the one-dimensional vector, for example, according to context-adaptive binary arithmetic coding (CABAC). The video encoder 200 may also entropy encode the values of syntax elements used to describe metadata associated with the encoded video data for use by the video decoder 300 when decoding the video data.

To perform CABAC, the video encoder 200 may assign a context within a context model to a symbol to be sent. The context may relate to, for example, whether the neighboring values of the symbol are zero values. The probability decision may be based on the context assigned to the symbol.

The video encoder 200 may also generate syntax data (such as block-based syntax data, picture-based syntax data, and sequence-based syntax data) for the video decoder 300, for example, in a picture header, a block header, a slice header, or other syntax data (such as a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS)). Similarly, the video decoder 300 may decode such syntax data to determine how to decode the corresponding video data.

In this way, the video encoder 200 can generate a bit stream that includes coded video data, such as syntax elements describing the partitioning of a picture into blocks (e.g., CUs) and prediction and/or residual information for the blocks. Finally, the video decoder 300 can receive the bit stream and decode the coded video data.

In general, the video decoder 300 performs a process that is the reverse of the process performed by the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 may use CABAC to decode the values of syntax elements for the bitstream in a manner substantially similar to, but reversed from, the CABAC encoding process of the video encoder 200. The syntax elements may define partitioning information for partitioning a picture into CTUs and partitioning each CTU according to a corresponding partitioning structure (e.g., a QTBT structure) to define CUs of the CTU. The syntax elements may also define prediction and residual information for a block (e.g., a CU) of video data.

The residual information may be represented by, for example, quantized transform coefficients. The video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of the block to reproduce a residual block for the block. The video decoder 300 uses the signaled prediction mode (intra-frame prediction or inter-frame prediction) and associated prediction information (e.g., motion information for inter-frame prediction) to form a prediction block for the block. The video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. The video decoder 300 may perform additional processing, such as performing a deblocking process to reduce visual artifacts along block boundaries.

In general, the present disclosure may involve "signaling" certain information (such as syntax elements). The term "signaling" can generally refer to the communication of values for syntax elements and/or other data used to decode the encoded video data. That is, the video encoder 200 can signal values for syntax elements in a bit stream. Generally, signaling refers to generating values in the bit stream. As mentioned above, the source device 102 can transmit the bit stream to the destination device 116 substantially in real time or not in real time (such as may occur when storing syntax elements to the storage device 112 for later retrieval by the destination device 116).

2A and 2B are conceptual diagrams showing an example quadtree binary tree (QTBT) structure 130 and a corresponding coding tree unit (CTU) 132. Solid lines represent quadtree separations, while dashed lines indicate binary tree separations. In each separation (i.e., non-leaf) node of the binary tree, a flag is signaled to indicate which separation type (i.e., horizontal or vertical) is used, where in this example, 0 indicates horizontal separation and 1 indicates vertical separation. For quadtree separations, since the quadtree node separates the block horizontally and vertically into 4 sub-blocks of equal size, there is no need to indicate the separation type. Thus, the video encoder 200 may encode, and the video decoder 300 may decode, syntax elements (such as separation information) for the region tree level (i.e., solid line) of the QTBT structure 130, and syntax elements (such as separation information) for the prediction tree level (i.e., dashed line) of the QTBT structure 130. The video encoder 200 may encode, and the video decoder 300 may decode, video data (such as prediction and transform data) for a CU represented by a terminal leaf node of the QTBT structure 130. The CTU may be partitioned using single-tree partitioning or dual-tree partitioning. In the case of single-tree partitioning, the chrominance components of the CTU and the luma components of the CTU have the same partitioning structure. In the case of dual-tree partitioning, the chrominance components of the CTU and the luma components of the CTU may have different partitioning structures.

2B may be associated with parameters defining the size of blocks corresponding to nodes at the first and second levels of the QTBT structure 130. The parameters may include a CTU size (indicating the size of the CTU 132 in a sample), a minimum quadtree size (MinQTSize, indicating the minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, indicating the maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, indicating the maximum allowed binary tree depth), and a minimum binary tree size (MinBTSize, indicating the minimum allowed binary tree leaf node size).

The root node of the QTBT structure corresponding to the CTU can have four child nodes at the first level of the QTBT structure, and each child node can be split according to the quadtree partitioning. That is, the nodes at the first level are leaf nodes (without child nodes) or have four child nodes. The instance of the QTBT structure 130 represents such a node as including a parent node and child nodes with solid line branches. If the nodes at the first level are not larger than the maximum allowed binary tree root node size (MaxBTSize), the nodes can be further partitioned by the corresponding binary tree. The binary tree separation of a node can be repeatedly calculated until the node resulting from the separation reaches the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). The example of QTBT structure 130 represents such nodes as having dashed branches. The binary leaf nodes are called coding units (CUs), which are used for prediction (e.g., intra-picture or inter-picture prediction) and transformation without any further partitioning. As discussed above, a CU may also be referred to as a "video block" or "block".

In an example of a QTBT partitioning structure, the CTU size is set to 128x128 (luminance sample and two corresponding 64x64 chroma samples), MinQTSize is set to 16x16, MaxBTSize is set to 64x64, MinBTSize (for both width and height) is set to 4, and MaxBTDepth is set to 4. Quadtree partitioning is first applied to the CTU to produce quadtree leaf nodes. Quadtree leaf nodes can have sizes from 16x16 (i.e., MinQTSize) to 128x128 (i.e., CTU size). If the quadtree leaf node is 128x128, then since the size exceeds MaxBTSize (i.e., 64x64 in this example), the leaf quadtree node will not be further separated by the binary tree. Otherwise, the quadtree leaf node will be further split by the binary tree. Therefore, the quadtree leaf node is also the root node for the binary tree and has a binary tree depth of 0. When the binary tree depth reaches MaxBTDepth (4 in this example), no further separation is allowed. A binary tree node with a width equal to MinBTSize (4 in this example) means that no further vertical separation (i.e., division of width) is allowed for the binary tree node. Similarly, a binary tree node with a height equal to MinBTSize means that no further horizontal separation (i.e., division of height) is allowed for the binary tree node. As mentioned above, the leaf nodes of the binary tree are called CUs and are further processed based on prediction and transformation without further partitioning.

In the HEVC Screen Content Coding (SCC) extension, ACT is used to self-adjust the predicted residue from one color space to a second color space, such as YCgCo space. By signaling an ACT flag, the two color spaces can be selected self-adjustingly. For example, a flag equal to one may indicate that the residue is encoded in the YCgCo space. Otherwise, a flag equal to 0 may indicate that the residue is encoded in the original color space. A similar technique is used in VVC, where the color space conversion is performed in the residue domain. Specifically, after the inverse transform for converting the residue from the YCgCo domain back to the original domain, an additional decoding unit (i.e., an inverse ACT unit) is introduced, which is described in more detail with respect to Figures 3 and 4.

The forward and inverse YCgCo color transformation matrices are as follows:

In addition, in order to compensate for the dynamic range changes of the residual signal before and after the color change, a QP adjustment of (-5, -5, -3) is applied to the transform residue. That is, the QP used for the quantization group can be adjusted for the block encoded with ACT. ACT is implemented in a manner such that the ACT applied at the video encoder 200 can be reversed by the video decoder 300. In order to compensate for the dynamic range changes of the residual signal before and after the color change, the QP adjustment can be applied to the transform residue by adding QP offsets to different color components. That is, the QP used in the first color space is modified before quantization or inverse quantization is performed in the second color space. The QP offset can be signaled as a high-level syntax.

In HEVC, the syntax element residual_adaptive_colour_transform_enabled_flag is signaled as part of the PPS to indicate whether ACT is enabled. If residual_adaptive_colour_transform_enabled_flag is true, the syntax elements pps_act_y_qp_offset_plus5, pps_act_cb_qp_offset_plus5, and pps_act_cr_qp_offset_plus3 for the QP offsets for ACT are signaled as part of the PPS. When residual_adaptive_colour_transform_enabled_flag is true, pps_slice_act_qp_offsets_present_flag is also signaled to indicate whether there is a slice level QP offset for ACT in the slice header. If pps_slice_act_qp_offset_present_flag is true, the syntax elements slice_act_y_qp_offset, slice_act_cb_qp_offset, and slice_act_cr_qp_offset are signaled in the slice header. The semantics of the QP offsets for ACT at the PPS and slice headers are as follows: pps_act_y_qp_offset_plus5, pps_act_cb_qp_offset_plus5, and pps_act_cr_qp_offset_plus3 are used to determine the offsets to be applied to the quantization parameter values qP derived in clause 8.6.2 for luma, Cb, and Cr components, respectively, when tu_residual_act_flag[ xTbY ][ yTbY ] is equal to 1. When not present, the values of pps_act_y_qp_offset_plus5, pps_act_cb_qp_offset_plus5, and pps_act_cr_qp_offset_plus3 are inferred to be equal to 0. The variable PpsActQpOffsetY is set equal to pps_act_y_qp_offset_plus5-5. The variable PpsActQpOffsetCb is set equal to pps_act_cb_qp_offset_plus5-5. The variable PpsActQpOffsetCr is set equal to pps_act_cb_qp_offset_plus3-3. slice_act_y_qp_offset, slice_act_cb_qp_offset, and slice_act_cr_qp_offset specify offsets to the quantization parameter values qP derived in clause 8.6.2 for luma, Cb, and Cr components, respectively. The values of slice_act_y_qp_offset, slice_act_cb_qp_offset, and slice_act_cr_qp_offset shall be in the range -12 to +12, inclusive. When not present, the values of slice_act_y_qp_offset, slice_act_cb_qp_offset, and slice_act_cr_qp_offset are inferred to be equal to 0. The value of PpsActQpOffsetY+slice_act_y_qp_offset shall be in the range -12 to +12, inclusive. The value of PpsActQpOffsetCb+slice_act_cb_qp_offset should be in the range of -12 to +12 (inclusive). The value of PpsActQpOffsetCr+slice_act_cr_qp_offset should be in the range of -12 to +12 (inclusive). If ACT is applied to blocks, the QP for luma blocks is derived by adding PpsActQpOffsetY+slice_act_y_qp_offset, the QP for Cb blocks is derived by adding PpsActQpOffsetCb+slice_act_cb_qp_offset, and the QP for Cr blocks is derived by adding PpsActQpOffsetCr+slice_act_cr_qp_offset.

According to the techniques of the present disclosure, video encoder 200 and video decoder 300 may be configured to perform flexible signaling of QP offsets.

According to one technique, there may be QP offset signaling for ACT in a slice header. The flag pps_slice_act_qp_offsets_present_flag may be used to control whether there is QP offset for ACT at the slice header. When ACT is enabled, pps_slice_act_qp_offsets_present_flag may be signaled at the picture parameter set. However, if the current slice uses more than one block partitioning tree structure, QP offset signaling for ACT at the slice header is disabled (skipped).

In the case of VVC (where qtbt_dual_tree_intra_flag is signaled to indicate whether the I slices in the sequence use a dual-tree block partitioning structure), the QP offset signal for ACT at the slice header is delivered as follows: if(pps_slice_act_qp_offsets_present_flag && !( slice_type = = I && qtbtt_dual_tree_intra_flag )){ slice_ act _y_qp_offset se(v) slice_ act _cb_qp_offset se(v) slice_ act _cr_qp_offset se(v) } se(v)

The syntax elements slice_act_y_qp_offset, slice_act_cb_qp_offset and slice_act_cr_qp_offset for ACT QP offsets are signaled only if all of the following are true: 1) pps_slice_act_qp_offsets_present_flag is true, which means that ACT QP offsets will be signaled at slice level, e.g., indicated at PPS level. 2) slice_type is not I or qtbt_dual_tree_intra_flag is false, which means that e.g., the slice is not an intra-frame prediction slice or dual-tree partitioning is not enabled.

According to some techniques of the present disclosure, video encoder 200 and video decoder 300 may signal the QP offset for ACT for each color component jointly for Y and Cb at the slice header as follows: Joint QP offset for Y and Cb components: if(pps_slice_act_qp_offsets_present_flag && !( slice_type = = I && qtbtt_dual_tree_intra_flag )){ slice_ act _y_cb_qp_offset se(v) slice_ act _cr_qp_offset se(v) } se(v) ˙Joint QP offset for Y and Cr components: if(pps_slice_act_qp_offsets_present_flag && !( slice_type = = I && qtbtt_dual_tree_intra_flag )){ slice_ act _y_cr_qp_offset se(v) slice_ act _cb_qp_offset se(v) } se(v) ˙Joint QP offset for Cb and Cr components: if(pps_slice_act_qp_offsets_present_flag && !( slice_type = = I && qtbtt_dual_tree_intra_flag )){ slice_ act _y_qp_offset se(v) slice_ act _cb_cr_qp_offset se(v) } se(v) ˙Joint QP offset for all color components: if(pps_slice_act_qp_offsets_present_flag && !( slice_type = = I && qtbtt_dual_tree_intra_flag )){ slice_ act _qp_offset se(v) } se(v)

According to some techniques of the present disclosure, the QP offset signaling for ACT in the slice header may not be modified relative to VVC Draft 7, but may be constrained such that the QP offset is zero if the current slice uses more than one block partitioning tree structure, for example, if the current slice uses both single-tree partitioning and double-tree partitioning.

According to some techniques of the present disclosure, in the case of lossless coding (e.g., for coding scenarios where the transform bypass flag is 1 in HEVC or where QP=4 in VVC), no QP offset for ACT is signaled. Specifically, when a CU is losslessly coded, ACT is not used for each CU. When a CU is losslessly coded, the CU level flag and the quantization group of coding units (QGCU) level flag described below may not be present in the bitstream.

According to the techniques of the present disclosure, the video encoder 200 and the video decoder 300 may be configured to encode and decode an enable flag for an ACT at the QGCU level.

According to some techniques of the present disclosure, whether to enable or disable ACT can be signaled in the case of a QGCU, which means that ACT can be applied on a QGCU basis. Once ACT is applied, the transformed residual coefficients (when performing a transform), residual samples (when performing a transform skip), and palette primitives (e.g., palette colors and escape primitives when using palette mode) within the QGCU can all be encoded in the color transform domain. In addition, a CU-level flag for enabling ACT may not be required. According to some techniques of the present disclosure, since ACT is a QGCU-level coding tool, there is no CU-level flag for switching ACT on/off, while according to other techniques of the present disclosure, the CU-level flag still exists to maintain the flexibility of switching ACT on/off with finer granularity (such as CU or TU level). According to the techniques of the present disclosure, the video encoder 200 and the video decoder 300 can be configured to perform QP clipping for ACT.

To ensure that the QP values for transformed residue samples, transform skipped residues, and palettes never go out of range, some techniques of the present disclosure may include clipping the resulting QP values after adjusting the QP values by ACT. Without loss of generality, the notations Δy, Δcb, and Δcr denote the QP adjustment values for the three color components, respectively (i.e., slice header QP offset + picture level QP offset when ACT is enabled for the current residue sample; otherwise, 0). ˙QP’y=Clip3(0,QPmax+QpBdOffset,QPy+QpBdOffset+Δy), ˙QP’cb=Clip3(0,QPmax+QpBdOffset,QPcr+QpBdOffset+Δcb), ˙QP’cr=Clip3(0,QPmax+QpBdOffset,QPcr+QpBdOffset+Δcr), where QPmax is the maximum QP value supported in the video coding standard (e.g., 51 for HEVC and 63 for VVC), QpBdOffset=6*(internal bit depth-8), and the function Clip3(a, b, c) clips the value of c to the range from a to b (inclusive). Note that according to some techniques of the present disclosure, for some video codecs that do not support flexible QP signaling for ACT, the corresponding Δy, Δcb, and Δcr values are predetermined. In this case, the QP offset values can be configured as follows: ˙Δy=-5, ˙Δcb=-5, ˙Δcr=-3.

According to some techniques of the present disclosure, QP pruning can be combined with QGCU level signaling, as described above with respect to the enable flag for ACT at the QGCU level. The delta QP (i.e., the difference between the original QP and the minimum allowed QP) range can be adjusted based on the value of Δy. Since the minimum value of the base QP is 0, the minimum value of QPy can be derived as follows: QPy_min+6*(internal bitmap depth-8)+Δy=0, and therefore: QPy_min=-6*(internal bitmap depth–8)–Δy. Therefore, the delta QP between the original QP (i.e., QPy) and the minimum allowed QP (i.e., QPy_min) can be derived. ΔQP=QPy_min–Qpy=-6*(internal bitmap depth–8)–Δy–QPy.

According to the techniques of the present disclosure, the video encoder 200 and the video decoder 300 can be configured to perform QP pruning for ACT when transform coding is skipped. According to some techniques of the present disclosure, when transform coding is not used, the minimum QP value cannot be as low as 0 to prevent signal expansion. The QP values derived above (i.e., QP’y, QP’cb, QP’cr) can be further adjusted as follows: ˙QP’y=Max(QP’y,M+6*(internal pixel depth-input bit depth)), ˙QP’cb=Max(QP’cb,M+6*(internal pixel depth-input bit depth)), ˙QP’cr=Max(QP’cr,M+6*(internal pixel depth-input bit depth)), Or, more precisely, in a standalone form, ˙QP’y=Clip3(M+6*(internal pixel depth-input bit depth),QPmax+QpBdO ffset,QPy+QpBdOffset+Δy), ˙QP’cb=Clip3(M+6*(internal bit depth-input bit depth),QPmax+QpBdOffset,QPcr+QpBdOffset+Δcb), ˙QP’cr=Clip3(M+6*(internal bit depth-input bit depth),QPmax+QpBdOffset,QPcr+QpBdOffset+Δcr), where M is the QP value corresponding to a quantization step size equal to (or closest to) 1 in the video codec (e.g., 4 in VVC).

Note that these QP values (i.e., QP’y, QP’cb, QP’cr) also apply to palette coded CUs.

According to some techniques of the present disclosure, QP pruning can be combined with QGCU-level signaling, as described above with respect to the enable flag for ACT at the QGCU level. The delta QP (i.e., the difference between the original QP and the minimum allowed QP) range can be adjusted based on the value of Δy. Since the minimum value of the base QP is M (e.g., 4), the minimum value of QPy can be derived as follows: QPy_min+6*(internal bit pixel depth-8)+Δy=M+6*(internal bit pixel depth-input bit depth), and therefore: QPy_min=M-6*(input bit depth-8)-Δy.

Therefore, the difference QP between the original QP (i.e., QPy) and the minimum allowed QP (i.e., QPy_min) can be derived. ΔQP=QPy_min-QPy=M-6*(internal bit depth-8)-Δy-QPy.

According to the techniques of the present disclosure, the video encoder 200 and the video decoder 300 may be configured to perform ACT for dual-tree block partitioning.

According to some techniques of the present disclosure, ACT can still be applied when dual-tree block partitioning is used. When dual-tree block partitioning is enabled, color components _C1 and _C2 can be encoded and reconstructed separately _from C0 . Under the assumption that the color component of _C0 is encoded and reconstructed earlier than other components of the same primitive, the forward color transform as described above can be reformulated as: , in is the reconstruction signal of C _0. The coding loop only uses the signal to notify C ₀ , and quantized signal.

In the backward color transform shown below, the decoding loop has the reconstructed values (i.e., , and ), and therefore the backward transform cannot be applied directly, since after decoding only , but don't know .

The formula can be obtained by and We can reformulate this by swapping to either side of the equation:

In some examples, C ₀ (and and ) may not be available to be coded jointly _with C1 and C2 . When this happens, the color conversion is performed on _the other two color components. Assign 0. Therefore, the forward and backward color transforms can be reformulated as follows: as well as , or in compact form, as follows: as well as .

Note that when pps_slice_act_qp_offsets_present_flag is enabled, each CU can have an enable flag for ACT. In addition, the italic branch conditions described in the syntax table above regarding the signaling of QP offsets can be redefined as follows. if(pps_slice_act_qp_offsets_present_flag) { if( slice_type != I||!qtbtt_dual_tree_intra_flag ) slice_ act _y_qp_offset se(v) slice_ act _cb_qp_offset se(v) slice_ act _cr_qp_offset se(v) } se(v)

Furthermore, according to some techniques of the present disclosure, the QP offset for ACT per color component may be signaled jointly for Y and Cb at the slice header as follows: Joint QP offset for Y and Cb components: if(pps_slice_act_qp_offsets_present_flag){ slice_ act _y_cb_qp_offset se(v) slice_ act _cr_qp_offset se(v) } se(v) ˙Joint QP offset for Y and Cr components: if(pps_slice_act_qp_offsets_present){ slice_ act _y_cr_qp_offset se(v) slice_ act _cb_qp_offset se(v) } se(v) ˙Joint QP offset for Cb and Cr components: if(pps_slice_act_qp_offsets_present_flag){ if( slice_type != I || !qtbtt_dual_tree_intra_flag ) slice_ act _y_qp_offset se(v) slice_ act _cb_cr_qp_offset se(v) } se(v) ˙Joint QP offset for all color components: if(pps_slice_act_qp_offsets_present_flag) { slice_ act _qp_offset se(v) } se(v)

According to the techniques of the present disclosure, the video encoder 200 and the video decoder 300 may be configured to use a separate QP offset for the joint-CbCr mode. That is, the video encoder 200 and the video decoder 300 may be configured to determine an ACT QP offset for a block based on whether the block is encoded using ACT and is encoded in a joint-chroma mode (e.g., joint-CbCr mode). For example, the video encoder 200 and the video decoder 300 may store a set of ACT QP offsets, where the set includes a first ACT QP offset for a luma residue component of the video data, a second ACT QP offset for a first chroma residue component of the video data, a third ACT QP offset for a second chroma residue component of the video data, and a fourth ACT QP offset for a jointly encoded chroma residue component. The fourth ACT QP offset may be different from one or both of the second ACT QP offset and the third ACT QP offset.

VVC draft 7 includes a joint CbCr mode, in which only one chroma residue block is encoded, which is denoted as CbCr residue. At the video decoder 300, after the CbCr residue is reconstructed, the Cb and Cr residues are derived according to the selected joint CbCr mode. In one of the joint CbCr modes (denoted as mode 2 in VVC), the Cr residue is set to be the same as the CbCr residue, and the Cb residue is set to Cb=Csign*Cr, where Csign can be 1 or -1, depending on the joint CbCr mode. If joint CbCr mode 2 is used for a coding unit, a separate QP offset specified for the CbCr residue can be applied.

According to the techniques of the present disclosure, the video encoder 200 and the video decoder 300 can be configured to use separate ACT QP offsets if joint CbCr mode 2 is applied to the ACT block for residual coding. Therefore, overall, there can be four ACT QP offsets, one for luma, one for Cb, one for Cr, and one for CbCr.

In some examples, a separate ACT QP offset for joint-CbCr mode 2 may be fixed to an integer value. In some examples, a separate ACT QP offset for joint-CbCr mode may be signaled like other ACT QP offsets. For example, pps_act_cb_cr_qp_offset_plus5 may be signaled in the picture parameter set like pps_act_cb_cr_qp_offset_plus5, and slice_act_cb_cr_qp_offset may be signaled in the slice header like slice_act_cr_qp_offset.

In some examples, separate ACT QP offsets for joint-CbCr mode (pps_act_cb_cr_qp_offset_plus5 and slice_act_cb_cr_qp_offset) may be signaled only when joint-CbCr mode is enabled at the SPS.

In some examples, a separate ACT QP offset for joint-CbCr mode may always be signaled even if joint-CbCr mode is not enabled at the SPS.

To implement the various techniques described above, the video encoder 200 may be configured to: determine a first chroma residue block for a first chroma component of a block of video data; determine a second chroma residue block for a second chroma component of a block of video data, wherein the first chroma residue block and the second chroma residue block are in a first color space; determine that the block of video data is encoded using an adaptive color transform (ACT); perform the ACT on the first chroma residue block to convert the first chroma residue block to a second color space; perform the ACT on the second chroma residue block; The method comprises performing an inverse ACT to convert the second chroma residue block to a second color space; determining that the block of video data is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for a first chroma component of the block and a second chroma component of the block; determining a single chroma residue block based on the converted first chroma residue block and the converted second chroma residue block; determining a QP for the block; determining an ACT for the block based on the block being encoded using ACT and being encoded in the joint chroma mode QP offset; determining an ACT QP for the block based on the QP and the ACT QP offset; and quantizing a single chroma residue block based on the ACT QP for the block.

To implement the various techniques described above, the video decoder 300 may be configured to: determine that a block of video data is encoded using ACT; determine that the block is encoded in a joint chroma mode where a single chroma residue block is encoded for a first chroma component of the block and a second chroma component of the block; determine a QP for the block; determine an ACT QP offset for the block based on the block being encoded using ACT and being encoded in a joint chroma mode; determine an ACT QP for the block based on the QP and the ACT QP offset; determine an ACT QP for the block based on the ACT QP for the block; A method for determining a single chroma residue block based on a QP; determining a first chroma residue block for a first chroma component based on the single chroma residue block, wherein the first chroma residue block is in a first color space; determining a second chroma residue block for a second chroma component based on the single chroma residue block, wherein the second chroma residue block is in the first color space; performing an inverse ACT on the first chroma residue block to convert the first chroma residue block to the second color space; and performing an inverse ACT on the second chroma residue block to convert the second chroma residue block to the second color space.

FIG. 3 is a block diagram illustrating an example video encoder 200 that may perform the techniques of the present disclosure. FIG. 3 is provided for purposes of explanation and should not be considered limiting of the techniques generally exemplified and described in the present disclosure. For purposes of explanation, the present disclosure describes the video encoder 200 in the context of video coding standards, such as the developing HEVC video coding standard and the H.266 video coding standard. However, the techniques of the present disclosure are not limited to such video coding standards and are generally applicable to video encoding and decoding.

In the example of Figure 3, the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residue generation unit 204, an ACT unit 205, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, an inverse ACT unit 213, a reconstruction unit 214, a filter unit 216, a decoded picture buffer (DPB) 218 and an entropy coding unit 220. Any or all of the video data memory 230, the mode selection unit 202, the residue generation unit 204, the transform processing unit 206, the quantization unit 208, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the filter unit 216, the DPB 218, and the entropy coding unit 220 may be implemented in one or more processors or in processing circuits. For example, the units of the video encoder 200 may be implemented as one or more circuits or logic elements, as part of a hardware circuit, or as part of a processor, ASIC, or FPGA. In addition, the video encoder 200 may include additional or alternative processors or processing circuits to perform these and other functions.

The video data memory 230 may store video data to be encoded by components of the video encoder 200. The video encoder 200 may receive video data stored in the video data memory 230 from, for example, the video source 104 ( FIG. 1 ). The DPB 218 may function as a reference picture memory that stores reference video data for use in making predictions of subsequent video data by the video encoder 200. The video data memory 230 and the DPB 218 may be formed of any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The video data memory 230 and DPB 218 can be provided by the same memory device or a separate memory device. In various examples, the video data memory 230 can be on the chip with other components of the video encoder 200 (as shown in the figure), or off the chip relative to those components.

In the present disclosure, references to the video data memory 230 should not be interpreted as limited to memory within the video encoder 200 (unless specifically described as such), or to memory external to the video encoder 200 (unless specifically described as such). Rather, references to the video data memory 230 should be understood as a reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data for the current block to be encoded). The memory 106 of FIG. 1 may also provide temporary storage for outputs from various units of the video encoder 200.

The various units of FIG. 3 are shown to assist in understanding the operations performed by the video encoder 200. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits represent circuits that provide specific functions and are pre-set with respect to the operations that may be performed. Programmable circuits represent circuits that may be programmed to perform a variety of tasks and provide flexible functionality with respect to the operations that may be performed. For example, a programmable circuit may execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the type of operation performed by the fixed-function circuit is generally immutable. In some instances, one or more of the cells may be distinct circuit blocks (fixed function or programmable), and in some instances, one or more of the cells may be integrated circuits.

The video encoder 200 may include an arithmetic logic unit (ALU), an elementary function unit (EFU), a digital circuit, an analog circuit, and/or a programmable core formed by a programmable circuit. In an example in which the operation of the video encoder 200 is performed using software executed by the programmable circuit, the memory 106 ( FIG. 1 ) may store instructions (e.g., object code) of the software received and executed by the video encoder 200, or another memory (not shown) within the video encoder 200 may store such instructions.

The video data memory 230 is configured to store the received video data. The video encoder 200 can retrieve the picture of the video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in the video data memory 230 can be the original video data to be encoded.

The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra-frame prediction unit 226. The mode selection unit 202 may include additional functional units that perform video prediction according to other prediction modes. As an example, the mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of the motion estimation unit 222 and/or the motion compensation unit 224), an affine unit, a linear model (LM) unit, etc.

The mode selection unit 202 typically coordinates multiple encoding passes to test combinations of encoding parameters and the resulting rate-distortion values for such combinations. The encoding parameters may include partitioning of a CTU into CUs, a prediction mode for a CU, a transform type for residual data of a CU, a quantization parameter for residual data of a CU, etc. The mode selection unit 202 may ultimately select a combination of encoding parameters that has a better rate-distortion value than other tested combinations.

The video encoder 200 may partition the picture retrieved from the video data memory 230 into a series of CTUs and encapsulate one or more CTUs in a slice. The mode selection unit 202 may partition the CTUs of the picture according to a tree structure (such as the QTBT structure or quadtree structure of HEVC described above). As described above, the video encoder 200 may partition the CTUs according to the tree structure to form one or more CUs. Such CUs may also be generally referred to as "video blocks" or "blocks".

Typically, the mode selection unit 202 also controls its components (e.g., the motion estimation unit 222, the motion compensation unit 224, and the intra-frame prediction unit 226) to generate a prediction block for a current block (e.g., the current CU, or the overlapping portion of a PU and a TU in HEVC). To perform inter-frame prediction for the current block, the motion estimation unit 222 may perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously coded pictures stored in the DPB 218). Specifically, the motion estimation unit 222 may calculate a value representing how similar a potential reference block will be to the current block, for example, based on the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean squared difference (MSD), etc. The motion estimation unit 222 may typically perform such calculations using the sample-by-sample difference between the current block and the reference block under consideration. The motion estimation unit 222 may identify the reference block with the lowest value resulting from such calculations, which indicates the reference block that most closely matches the current block.

The motion estimation unit 222 may form one or more motion vectors (MVs) that define the position of the reference block in the reference picture relative to the position of the current block in the current picture. The motion estimation unit 222 may then provide the motion vectors to the motion compensation unit 224. For example, for unidirectional inter-frame prediction, the motion estimation unit 222 may provide a single motion vector, while for bidirectional inter-frame prediction, the motion estimation unit 222 may provide two motion vectors. The motion compensation unit 224 may then use the motion vectors to generate a predicted block. For example, the motion compensation unit 224 may use the motion vectors to retrieve data for the reference block. As another example, if the motion vector has fractional sample precision, the motion compensation unit 224 may interpolate the values for the prediction block according to one or more interpolation filters. In addition, for bidirectional inter-frame prediction, the motion compensation unit 224 may retrieve data for two reference blocks identified by the corresponding motion vectors and combine the retrieved data, for example, via sample-by-sample averaging or weighted averaging.

As another example, for intra-frame prediction or intra-frame prediction coding, the intra-frame prediction unit 226 can generate a prediction block based on samples adjacent to the current block. For example, for a directional mode, the intra-frame prediction unit 226 can generally mathematically combine the values of the adjacent samples and fill the calculated values across the current block in a defined direction to generate the prediction block. As another example, for a DC mode, the intra-frame prediction unit 226 can calculate the average of the adjacent samples of the current block and generate the prediction block to include the resulting average for each sample of the prediction block.

The mode selection unit 202 provides the prediction block to the residue generation unit 204. The residue generation unit 204 receives the original, uncoded version of the current block from the video data memory 230 and receives the prediction block from the mode selection unit 202. The residue generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines a residue block for the current block. In some examples where the video data is encoded in a joint chroma mode, the residue generation unit 204 may decide a single chroma residue block from two separate chroma residue blocks. In some examples, the residue generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

In an example where the mode selection unit 202 partitions the CU into PUs, each PU can be associated with a luma prediction unit and a corresponding chroma prediction unit. The video encoder 200 and the video decoder 300 can support PUs of various sizes. As noted above, the size of the CU can represent the size of the luma coding block of the CU, and the size of the PU can represent the size of the luma prediction unit of the PU. Assuming that the size of a particular CU is 2Nx2N, the video encoder 200 can support PU sizes of 2Nx2N or NxN for intra-frame prediction, and 2Nx2N, 2NxN, Nx2N, NxN, or similar symmetric PU sizes for inter-frame prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter-frame prediction.

In an example where the mode selection unit 202 does not further partition the CU into PUs, each CU may be associated with a luma coding block and a corresponding chroma coding block. As described above, the size of the CU may represent the size of the luma coding block of the CU. The video encoder 200 and the video decoder 300 may support CU sizes of 2Nx2N, 2NxN, or Nx2N.

For other video coding techniques (such as intra-block copy mode coding, affine mode coding, and linear model (LM) mode coding, to name a few), the mode selection unit 202 generates a prediction block for the current block being encoded via a corresponding unit associated with the coding technique. In some examples (such as palette mode coding), the mode selection unit 202 may not generate a prediction block, but instead generate syntax elements indicating how to reconstruct the block based on the selected palette. In this mode, the mode selection unit 202 can provide these syntax elements to the entropy coding unit 220 for encoding.

As described above, the residue generation unit 204 receives video data for a current block and a corresponding predicted block. Subsequently, the residue generation unit 204 generates a residue block for the current block. To generate the residue block, the residue generation unit 204 calculates a sample-by-sample difference between the predicted block and the current block. In a scene in which ACT is enabled, the ACT unit 205 may perform ACT on the residue block to convert the residue block from a first color space to a second color space. In a scene in which ACT is not enabled, the ACT unit 205 may act as a pass-through unit that does not change the residue block output by the residue generation unit 204.

The transform processing unit 206 applies one or more transforms to the residue block to generate a block of transform coefficients (referred to herein as a "transform coefficient block"). The transform processing unit 206 can apply various transforms to the residue block to form the transform coefficient block. For example, the transform processing unit 206 can apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residue block. In some examples, the transform processing unit 206 can perform a variety of transforms on the residue block, such as a primary transform and a secondary transform (such as a rotation transform). In some examples, the transform processing unit 206 does not apply a transform to the residual block.

The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to generate a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients of the transform coefficient block according to the QP value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU.

For a block of video data encoded in a joint chroma mode and using ACT, the quantization unit 208 may determine an ACT QP offset for the block based on the block being encoded using ACT and being encoded in a joint chroma mode, and determine an ACT QP for the block based on the QP value and the ACT QP offset. Thus, for a block of video data encoded in a joint chroma mode and using ACT, the quantization unit 208 may quantize the block using the ACT QP value instead of the QP value. Quantization may cause information loss, and therefore, the quantized transform coefficients may have lower precision than the original transform coefficients generated by the transform processing unit 206.

The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform to the quantized transform coefficient block, respectively, to reconstruct the residue block from the transform coefficient block. For a block of video data encoded in a joint chroma mode and using ACT, the inverse quantization unit 210 may determine an ACT QP offset for the block based on that the block is encoded using ACT and is encoded in the joint chroma mode, and determine an ACT QP for the block based on the QP value and the ACT QP offset. Therefore, for a block of video data encoded in a joint chroma mode and using ACT, the inverse quantization unit 210 may use the ACT QP value instead of the QP value to inverse quantize the block.

In the scene where ACT is enabled, the inverse ACT unit 213 can perform inverse ACT on the reconstructed residual block to convert the residual block from the second color space back to the first color space. In the scene where ACT is not enabled, the inverse ACT unit 213 can act as a pass-through unit that does not change the reconstructed residual block output by the inverse transform processing unit 212.

The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (albeit potentially with some degree of distortion) based on the reconstructed residual block and the predicted block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the predicted block generated by the mode selection unit 202 to generate the reconstructed block.

The filter unit 216 may perform one or more filter operations on the reconstructed blocks. For example, the filter unit 216 may perform a deblocking operation to reduce block effect artifacts along the edges of the CU. In some examples, the operation of the filter unit 216 may be skipped.

The video encoder 200 stores the reconstructed blocks in the DPB 218. For example, in instances where operation of the filter unit 216 is not required, the reconstruction unit 214 may store the reconstructed blocks in the DPB 218. In instances where operation of the filter unit 216 is required, the filter unit 216 may store the filtered reconstructed blocks in the DPB 218. The motion estimation unit 222 and the motion compensation unit 224 may retrieve a reference picture formed by the reconstructed (and potentially filtered) blocks from the DPB 218 to perform inter-frame prediction on blocks of subsequently encoded pictures. Additionally, the intra-frame prediction unit 226 may use the reconstructed blocks of the current picture in the DPB 218 to perform intra-frame prediction on other blocks in the current picture.

In general, entropy coding unit 220 may entropy code syntax elements received from other functional components of video coder 200. For example, entropy coding unit 220 may entropy code quantized transform coefficient blocks from quantization unit 208. As another example, entropy coding unit 220 may entropy code prediction syntax elements (e.g., motion information for inter-frame prediction or intra-frame mode information for intra-frame prediction) from mode selection unit 202. Entropy coding unit 220 may perform one or more entropy coding operations on syntax elements, which are another example of video data, to generate entropy-coded data. For example, the entropy coding unit 220 may perform a context-adjusting variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adjusting binary arithmetic coding (SBAC) operation, a probability interval partitioning entropy (PIPE) coding operation, an exponential Columbus coding operation, or another type of entropy coding operation on the data. In some examples, the entropy coding unit 220 may operate in a bypass mode in which syntax elements are not entropy coded.

The video encoder 200 may output a bitstream including entropy-coded syntax elements required for reconstructing a slice or a block of a picture. Specifically, the entropy coding unit 220 may output a bitstream.

The above operations are described with respect to blocks. Such descriptions should be understood as operations for luma coding blocks and/or chroma coding blocks. As described above, in some instances, the luma coding blocks and chroma coding blocks are the luma components and chroma components of a CU. In some instances, the luma coding blocks and chroma coding blocks are the luma components and chroma components of a PU.

In some examples, operations performed with respect to luma coding blocks do not need to be repeated for chroma coding blocks. As one example, operations for identifying motion vectors (MVs) and reference pictures for luma coding blocks do not need to be repeated to identify MVs and reference pictures for chroma blocks. Rather, the MVs for luma coding blocks may be scaled to determine MVs for chroma blocks, and the reference pictures may be the same. As another example, the intra-frame prediction process may be the same for luma coding blocks and chroma coding blocks.

The video encoder 200 represents an example of an apparatus configured to encode video data, the apparatus comprising: a memory configured to store the video data; and one or more processing units implemented in circuitry and configured to: determine one or more QP offset values to be included in a slice header; in response to determining that the one or more QP offset values are to be included in the slice header, generate a flag having a first value to be included in a parameter set, wherein the flag The first value of the flag indicates that the one or more QP offset values are included in the slice header, and the second value of the flag indicates that the one or more QP offset values are not included in the slice header; in response to determining that the one or more QP offset values are included in the slice header, the one or more QP offset values are generated to be included in the slice header; based on the one or more QP offset values, self-adjusting color transform is performed on the residual data to determine the color transformed residual data. The video encoder 200 can be configured to: determine whether to enable or disable self-adjusting color transform for a quantization group of a coding unit (QGCU); in response to determining that self-adjusting color transform is enabled for the QGCU, generate a flag indicating whether self-adjusting color transform is enabled or disabled for the QGCU to be included in the video data; and process sample values of the QGCU in the color transform domain.

FIG. 4 is a block diagram illustrating an example video decoder 300 that can perform the techniques of the present disclosure. FIG. 4 is provided for purposes of explanation and does not limit the techniques generally exemplified and described in the present disclosure. For purposes of explanation, the present disclosure describes the video decoder 300 according to the techniques of JEM, VVC, and HEVC. However, the techniques of the present disclosure can be performed by video coding devices configured for other video coding standards.

4, the video decoder 300 includes a coded picture buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, an inverse ACT unit 309, a reconstruction unit 310, a filter unit 312, and a decoded picture buffer (DPB) 134. Any one or all of the CPB memory 320, the entropy decoding unit 302, the prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, the filter unit 312, and the DPB 134 may be implemented in one or more processors or in a processing circuit. For example, the units of the video decoder 300 may be implemented as one or more circuits or logic elements, as part of a hardware circuit, or as part of a processor, ASIC or FPGA. In addition, the video decoder 300 may include additional or alternative processors or processing circuits to perform these and other functions.

The prediction processing unit 304 includes a motion compensation unit 316 and an intra-frame prediction unit 318. The prediction processing unit 304 may include an addition unit that performs prediction according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of the motion compensation unit 316), an affine unit, a linear model (LM) unit, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

CPB memory 320 can store video data, such as an encoded video bit stream, to be decoded by components of video decoder 300. For example, the video data stored in CPB memory 320 can be obtained from computer-readable medium 110 (FIG. 1). CPB memory 320 can include a CPB that stores encoded video data (e.g., syntax elements) from the encoded video bit stream. In addition, CPB memory 320 can store video data other than syntax elements of encoded pictures, such as temporary data representing output from various units of video decoder 300. DPB 314 typically stores decoded pictures, which the video decoder 300 can output and/or use as reference video data when decoding subsequent data or pictures of the encoded video bit stream. CPB memory 320 and DPB 314 can be formed by any of a variety of memory devices, such as DRAM, including SDRAM, MRAM, RRAM or other types of memory devices. CPB memory 320 and DPB 314 can be provided by the same memory device or a separate memory device. In various embodiments, CPB memory 320 can be on-chip with other components of video decoder 300, or off-chip relative to those components.

Additionally or alternatively, in some examples, the video decoder 300 may retrieve the encoded video data from the memory 120 ( FIG. 1 ). That is, the memory 120 may utilize the CPB memory 320 to store the data as discussed above. Similarly, when some or all of the functions of the video decoder 300 are implemented in software to be executed by the processing circuits of the video decoder 300, the memory 120 may store instructions to be executed by the video decoder 300.

The various units illustrated in FIG. 4 are shown to assist in understanding the operations performed by the video decoder 300. The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Similar to FIG. 3 , fixed-function circuits represent circuits that provide specific functions and are pre-set with respect to the operations that may be performed. Programmable circuits represent circuits that may be programmed to perform a variety of tasks and provide flexible functionality with respect to the operations that may be performed. For example, a programmable circuit may execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed-function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the type of operation performed by the fixed-function circuit is generally immutable. In some instances, one or more of the cells may be distinct circuit blocks (fixed function or programmable), and in some instances, one or more of the cells may be integrated circuits.

The video decoder 300 may include an ALU, an EFU, a digital circuit, an analog circuit, and/or a programmable core formed by a programmable circuit. In an example where the operation of the video decoder 300 is performed by software executed on the programmable circuit, an on-chip or off-chip memory may store instructions (e.g., object code) of the software received and executed by the video decoder 300.

The entropy decoding unit 302 may receive the encoded video data from the CPB and perform entropy decoding on the video data to reproduce the syntax elements. The prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310 and the filter unit 312 may generate decoded video data based on the syntax elements extracted from the bit stream.

Typically, the video decoder 300 reconstructs the picture on a block-by-block basis. The video decoder 300 may perform the reconstruction operation on each block individually (where the block currently being reconstructed (i.e., decoded) may be referred to as the "current block").

The entropy decoding unit 302 may entropy decode syntax elements of quantized transform coefficients defining the block of quantized transform coefficients and transform information such as a QP and/or a transform mode indication. The inverse quantization unit 306 may use the QP associated with the block of quantized transform coefficients to determine a degree of quantization and, likewise, a degree of inverse quantization to be applied by the inverse quantization unit 306. For a block of video data encoded in joint chroma mode and using ACT, the inverse quantization unit 306 may determine an ACT QP offset for the block based on that the block is encoded using ACT and is encoded in joint chroma mode, and determine an ACT QP for the block based on the QP value and the ACT QP offset. Therefore, for a block of video data encoded in joint chroma mode and using ACT, the inverse quantization unit 306 can use the ACT QP value instead of the QP value to inverse quantize the block. The inverse quantization unit 306 can, for example, perform a bitwise left shift operation to inverse quantize the quantized transform coefficients. The inverse quantization unit 306 can thereby form a transform coefficient block including the transform coefficients.

After the inverse quantization unit 306 forms the transform coefficient block, the inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, the inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotation transform, an inverse directional transform, or another inverse transform to the transform coefficient block.

In the scenario where ACT is enabled, the inverse ACT unit 309 can perform inverse ACT on the residue block to convert the residue block from the second color space back to the first color space. In the scenario where ACT is not enabled, the inverse ACT unit 309 can act as a pass-through unit that does not change the residue block output by the inverse transform processing unit 308.

In addition, the prediction processing unit 304 generates a prediction block based on the prediction information syntax element entropy decoded by the entropy decoding unit 302. For example, if the prediction information syntax element indicates that the current block is predicted through inter-frame, the motion compensation unit 316 can generate the prediction block. In this case, the prediction information syntax element can indicate a reference picture in the DPB 314 from which the reference block is to be retrieved, and a motion vector identifying the position of the reference block in the reference picture relative to the position of the current block in the current picture. The motion compensation unit 316 can generally perform the inter-frame prediction process in a manner substantially similar to that described with respect to the motion compensation unit 224 (Figure 3).

As another example, if the prediction information syntax element indicates that the current block is predicted intra-frame, the intra-frame prediction unit 318 can generate a prediction block according to the intra-frame prediction mode indicated by the prediction information syntax element. Again, the intra-frame prediction component 318 can generally perform the intra-frame prediction process in a manner substantially similar to that described with respect to the intra-frame prediction unit 226 (FIG. 3). The intra-frame prediction unit 318 can retrieve data of neighboring samples of the current block from the DPB 314.

The reconstruction unit 310 can use the prediction block and the residual block to reconstruct the current block. For example, the reconstruction unit 310 can add the samples of the residual block to the corresponding samples of the prediction block to reconstruct the current block.

The filter unit 312 may perform one or more filter operations on the reconstructed block. For example, the filter unit 312 may perform a deblocking operation to reduce block effect artifacts along the edges of the reconstructed block. The operations of the filter unit 312 may not necessarily be performed in all instances.

The video decoder 300 may store the reconstructed blocks in the DPB 314. For example, in instances where the operation of the filter unit 312 is not performed, the reconstruction unit 310 may store the reconstructed blocks in the DPB 314. In instances where the operation of the filter unit 312 is performed, the filter unit 312 may store the filtered reconstructed blocks in the DPB 314. As discussed above, the DPB 314 may provide reference information (such as samples of the current picture for intra-frame prediction and previously decoded pictures for subsequent motion compensation) to the prediction processing unit 304. In addition, the video decoder 300 can output decoded pictures (e.g., decoded video) from the DPB 314 for subsequent presentation on a display device such as the display device 118 of Figure 1.

In this manner, the video decoder 300 represents an example of a video decoding device comprising: a memory configured to store video data; and one or more processing units implemented in circuitry and configured to: receive a flag in a parameter set, wherein a first value of the flag indicates that one or more QP offset values are included in a slice header, and a second value of the flag indicates that the one or more QP offset values are not included in the slice header; in response to determining that the flag has the first value, receive the one or more QP offset values in the slice header; and perform a self-adjusting color transform on the residual data based on the one or more QP offset values. The video decoder 300 may additionally or alternatively be configured to: receive a flag at a quantization group (QGCU) level of a coding unit, the flag indicating whether self-adjusting color transform is enabled or disabled for the QGCU; and in response to determining that the flag indicates that self-adjusting color transform is enabled for the QGCU, process sample values of the QGCU in the color transform domain.

FIG5 is a flow chart showing an example method for encoding a current block. The current block may include a current CU. Although described with respect to the video encoder 200 (FIGS. 1 and 3), it should be understood that other devices may be configured to perform methods similar to those of FIG5.

In this example, the video encoder 200 initially predicts the current block (350). For example, the video encoder 200 can form a predicted block for the current block. The video encoder 200 can then calculate a residue block for the current block (352). To calculate the residue block, the video encoder 200 can calculate the difference between the original uncoded block and the predicted block for the current block. For some blocks, the video encoder 200 can also calculate the residue block by performing ACT, as described above. The video encoder 200 can then transform and quantize the coefficients of the residue block (354). Next, the video encoder 200 can scan the quantized transform coefficients of the residual block (356). During or after scanning, the video encoder 200 can entropy encode the transform coefficients (358). For example, the video encoder 200 can encode the transform coefficients using CAVLC or CABAC. The video encoder 200 can then output the entropy encoded data of the block (360).

FIG6 is a flow chart illustrating an example method for decoding a current block of video data. The current block may include a current CU. Although described with respect to video decoder 300 (FIGS. 1 and 4), it should be understood that other devices may be configured to perform methods similar to those of FIG6.

The video decoder 300 may receive entropy coded data for a current block (e.g., entropy coded prediction information and entropy coded data for coefficients of a residue block corresponding to the current block) (370). The video decoder 300 may entropy decode the entropy coded data to determine prediction information for the current block and reproduce coefficients of the residue block (372). The video decoder 300 may predict the current block (374), e.g., using an intra-frame or inter-frame prediction mode as indicated by the prediction information for the current block, to calculate a prediction block for the current block. The video decoder 300 may then inverse scan the reproduced coefficients (376) to create a block of quantized transform coefficients. The video decoder 300 may then inverse quantize and inverse transform the transform coefficients to produce a residue block (378). For some blocks, the video decoder may also perform ACT as described above to produce a residue block. Finally, the video decoder 300 may decode the current block by combining the prediction block and the residue block (380).

FIG. 7 is a flow chart illustrating an example method for decoding a current block of video data. The current block may include a current CU. Although described with respect to video decoder 300 (FIGS. 1 and 4), it should be understood that other devices may be configured to perform methods similar to those of FIG. 7.

The video decoder 300 determines that a block of video data is coded using ACT (400). For example, the video decoder 300 may determine that the block of video data is coded using ACT by receiving a CU level flag indicating that ACT is enabled for the block of video data.

The video decoder 300 determines that the block is coded in a joint chroma mode (402). As described above, for the joint chroma mode, a single chroma residue block may be coded for a first chroma component of the block and a second chroma component of the block. The video decoder 300 may determine that the block is coded in a joint chroma mode by, for example, receiving a CU-level syntax element indicating that the joint chroma mode is enabled for the block.

The video decoder 300 determines a QP for the block (404). For example, the video decoder 300 may determine the QP for the block at a quantization group level. The quantization group may have the same size as the block, or may be larger or smaller than the block, so that the QP for the block may be one of multiple QPs for the block or apply to multiple blocks.

The video decoder 300 determines an ACT QP offset for the block based on the block being encoded using ACT and being encoded in a joint chroma mode (406). For example, the video decoder 300 may store a set of ACT QP offsets, where the set includes a first ACT QP offset for a luma residue component of the video data, a second ACT QP offset for a first chroma residue component of the video data, a third ACT QP offset for a second chroma residue component of the video data, and a fourth ACT QP offset for a jointly encoded chroma residue component. To determine the ACT QP offset for the block based on the block being coded using ACT and coded in joint chroma mode, the video decoder 300 can be configured to, in response to the block being coded using ACT and coded in joint chroma mode, set the value for the ACT QP offset to the value for the fourth ACT QP offset. To determine the ACT QP offset for the block based on the block being coded using ACT and coded in joint chroma mode, the video decoder 300 can be configured to set the ACT QP offset to a fixed integer value. In this context, fixed can, for example, mean that the ACT QP offset is defined in a transcoder executed by the video decoder 300.

The video decoder 300 determines an ACT QP for the block based on the QP and the ACT QP offset (408). The video decoder 300 determines a single chroma residue block based on the ACT QP for the block (410). That is, the video decoder 300 may dequantize the block of quantized transform coefficients to determine the single chroma residue block.

The video decoder 300 determines a first chroma residue block for a first chroma component based on the single chroma residue block (412). The video decoder 300 determines a second chroma residue block for a second chroma component based on the single chroma residue block (414). The first chroma residue block and the second chroma residue block may be in a first color space, such as a YCgCo color space.

To determine a first chroma residue block for a first chroma component based on a single chroma residue block, the video decoder 300 may, for example, set the sample values for the first chroma residue block to be equal to the values of corresponding samples in the single chroma residue block. To determine a second chroma residue block for a second chroma component based on a single chroma residue block, the video decoder 300 may set the sample values for the second chroma residue block to be equal to the values of corresponding samples in the first chroma residue block multiplied by negative one.

The video decoder 300 performs an inverse ACT on the first chroma residue block to convert the first chroma residue block to a second color space (416). The video decoder 300 performs an inverse ACT on the second chroma residue block to convert the second chroma residue block to a second color space (418). The video decoder 300 may add the converted first chroma residue block to the first predicted chroma block to determine a first reconstructed chroma block; add the converted second chroma residue block to the second predicted chroma block to determine a second reconstructed chroma block; and output the first reconstructed chroma block and the second reconstructed chroma block.

The video decoder 300 may also determine that a second block of video data is encoded using ACT; determine that the second block is not encoded in joint chroma mode; determine a QP for the second block; determine a second ACT QP offset for a first chroma component of the second block based on that the second block is encoded using ACT and is not encoded in joint chroma mode; and determine a third ACT QP offset for a second chroma component of the second block based on that the second block is encoded using ACT and is not encoded in joint chroma mode, wherein at least one of the second ACT QP offset and the third ACT QP offset is different from the first ACT QP offset.

FIG8 is a flow chart showing an example method for encoding a current block. The current block may include a current CU. Although described with respect to the video encoder 200 (FIGS. 1 and 3), it should be understood that other devices may be configured to perform methods similar to those of FIG8.

The video encoder 200 determines a first chroma residue block for a first chroma component of a block of video data (420). The video encoder 200 determines a second chroma residue block for a second chroma component of the block of video data, wherein the first chroma residue block and the second chroma residue block are in a first color space (422). The video encoder 200 determines that the block of video data is encoded using ACT (424). The video encoder 200 performs ACT on the first chroma residue block to convert the first chroma residue block to a second color space (426). The video encoder 200 performs an inverse ACT on the second chroma residue block to convert the second chroma residue block to a second color space (428). For example, the second color space can be a YCgCo color space. The video encoder 200 determines that the block of video data is encoded in a joint chroma mode (430). In the joint chroma mode, the video encoder 200 encodes a single chroma residue block for a first chroma component of the block and a second chroma component of the block. The video encoder 200 determines a single chroma residue block based on the converted first chroma residue block and the converted second chroma residue block (432). The video encoder 200 determines a QP for the block (434).

The video encoder 200 determines an ACT QP offset for the block based on the block being encoded using ACT and encoded in a joint chroma mode (436). The video encoder 200 may store a set of ACT QP offsets, wherein the set of ACT QP offsets includes a first ACT QP offset for a luma residue component of the video data, a second ACT QP offset for a first chroma residue component of the video data, a third ACT QP offset for a second chroma residue component of the video data, and a fourth ACT QP offset for a jointly encoded chroma residue component. To determine the ACT QP offset for the block based on the block being encoded using ACT and being encoded in joint-chroma mode, the video encoder 200 may set the value for the ACT QP offset to the value for the fourth ACT QP offset in response to the block being encoded using ACT and being encoded in joint-chroma mode. The method of claim 12, wherein to determine the ACT QP offset for the block based on the block being encoded using ACT and being encoded in joint-chroma mode, the video encoder 200 may set the ACT QP offset to a fixed integer value.

The video encoder 200 determines an ACT QP for the block based on the QP and the ACT QP offset (438). The video encoder 200 quantizes the single chroma residue block based on the ACT QP for the block (440). The video encoder 200 may then transform the quantized single chroma residue block to generate transform coefficients and output syntax elements for identifying the transform coefficients.

The following clauses describe example apparatus and processes based on the video encoder 200 and the video decoder 300 and the techniques discussed above.

Clause 1: A method of decoding video data comprises: receiving a flag in a parameter set, wherein a first value of the flag indicates that one or more quantization parameter (QP) offset values are included in a slice header, and a second value of the flag indicates that the one or more QP offset values are not included in the slice header; in response to determining that the flag has the first value, receiving the one or more QP offset values in the slice header; and performing a self-adjusting color transform on residual data based on the one or more QP offset values.

Clause 2: The method of clause 1, further comprising: receiving the flag in the parameter set in response to determining to enable self-adjusting color transformation.

Clause 3: The method of clause 1 or 2, further comprising: further responsive to determining that the slice type of the slice having the slice header is not an I slice, receiving the one or more QP offset values in the slice header.

Clause 4: The method of clause 1 or 2, further comprising: further responsive to determining that the slice having the slice header does not use dual-tree block partitioning to receive the one or more QP offset values in the slice header.

Clause 5: A method as described in any of clauses 1-4, wherein the parameter set is a picture parameter set.

Clause 6: The method as described in any one of clauses 1-5 further includes: determining the value of the quantized transform coefficient; inverse quantizing the values of the quantized transform coefficient to determine the value of the dequantized transform coefficient; inverse transforming the dequantized transform coefficient to determine the residual data.

Clause 7: A method as described in any of clauses 1-5, wherein the residual data includes residual data of skipped transformations.

Clause 8: A method for decoding video data comprises: receiving a flag at a quantization group (QGCU) level of a coding unit, the flag indicating whether self-adjusting color transform is enabled or disabled for the QGCU; and in response to determining that the flag indicates that self-adjusting color transform is enabled for the QGCU, processing sample values of the QGCU in a color transform domain.

Clause 9: A method of decoding video data comprises: determining that a residue block of the video data is encoded in a joint CbCr mode; receiving a joint CbCr offset value; and performing a self-adjusting color transform on the residue data based on the joint CbCr offset value.

Clause 10: The method as described in Clause 8, further comprising any one or combination of Clauses 1-8.

Clause 11: An apparatus for encoding video data, the apparatus comprising one or more components for performing a method as described in any one of clauses 1-10.

Clause 12: An apparatus as described in clause 11, wherein the one or more components include one or more processors implemented in circuitry.

Clause 13: The apparatus as described in any one of Clauses 11 and 12 further comprises: a memory for storing the video data.

Clause 14: The apparatus of any of clauses 11-13, further comprising: a display configured to display the decoded video data.

Clause 15: A device as described in any of clauses 11-14, wherein the device comprises one or more of the following: a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

Clause 16: An apparatus as described in any of Clauses 6-15, wherein the apparatus includes a video decoder.

Clause 17: A method for encoding video data comprises: determining one or more quantization parameter (QP) offset values to be included in a slice header; in response to determining that the one or more QP offset values are included in the slice header, generating a flag having a first value to be included in a parameter set, wherein the first value of the flag indicates that the one or more QP offset values are included in the slice header, and the second value of the flag indicates that the one or more QP offset values are not included in the slice header; in response to determining that the one or more QP offset values are included in the slice header, generating the one or more QP offset values to be included in the slice header; performing a self-adjusting color transform on residue data based on the one or more QP offset values to determine color transformed residue data.

Clause 18: The method of clause 17, further comprising: generating the flag in response to determining to enable self-adjusting color transformation for inclusion in the parameter set.

Clause 19: The method of clause 17 or 18, further comprising: further responsive to determining that the slice type of the slice having the slice header is not an I slice to generate the one or more QP offset values for inclusion in the slice header.

Clause 20: The method of clause 17 or 18, further comprising: further responsive to determining that the slice having the slice header does not use dual-tree block partitioning to generate the one or more QP offset values for inclusion in the slice header.

Clause 21: A method as described in any of clauses 17-20, wherein the parameter set is a picture parameter set.

Clause 22: A method as described in any one of clauses 17-21, further comprising: transforming the color transformed residual data to determine transformation coefficients; quantizing the transformation coefficients; and signaling the quantized transformation coefficients in the video data.

Clause 23: A method as described in any one of clauses 17-22, further comprising: signaling color-converted residual data in the video data.

Clause 24: A method for encoding video data comprises: determining whether to enable or disable self-adjusting color transform for a quantization group of coding units (QGCU); in response to determining to enable self-adjusting color transform for the QGCU, generating a flag indicating whether to enable or disable self-adjusting color transform for the QGCU for inclusion in the video data; and processing sample values of the QGCU in a color transform domain.

Clause 25: The method as described in Clause 24, further comprising any one or combination of Clauses 16-22.

Clause 26: An apparatus for encoding video data, the apparatus comprising one or more components for performing a method as described in any one of clauses 17-25.

Clause 27: An apparatus as described in clause 26, wherein the one or more components include one or more processors implemented in circuitry.

Clause 28: The apparatus as described in any one of Clauses 26 and 27 further comprises: a memory for storing the video data.

Clause 29: An apparatus as described in any of clauses 26-28, wherein the apparatus comprises one or more of the following: a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

Clause 30: An apparatus as described in any of clauses 26-29, wherein the apparatus comprises a video encoder.

Clause 31: A computer-readable storage medium having instructions stored thereon, which instructions, when executed, cause one or more processors to perform a method as described in any of clauses 1-10 or 17-25.

It is to be appreciated that, depending on the example, certain actions or events of any technique described herein may be performed in a different order, may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary to practice the techniques). In addition, in some examples, actions or events may be performed concurrently rather than sequentially, for example, via multithreading, interrupt handling, or multiple processors.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted via a computer-readable medium as one or more instructions or codes and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to tangible media such as data storage media, or communication media, which includes, for example, any media that facilitates the transfer of a computer program from one place to another according to a communication protocol. In this manner, computer-readable media may generally correspond to (1) non-transitory, tangible computer-readable storage media, or (2) communications media such as signals or carrier waves. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to obtain instructions, code and/or data structures for implementing the techniques described in this disclosure. A computer program product may include computer-readable media.

By way of example, and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and can be accessed by a computer. In addition, any connection is properly termed a computer-readable medium. For example, if coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies (such as infrared, radio, and microwave) are used to transmit commands from a website, server, or other remote source, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies (such as infrared, radio, and microwave) are included in the definition of media. However, it should be understood that computer-readable storage media and data storage media do not include connections, carriers, signals, or other temporary media, but instead refer to non-temporary tangible storage media. As used herein, magnetic disk and optical disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where magnetic disk usually copies data magnetically and optical disc uses laser to copy data optically. Combinations of the above should also be included in the scope of computer-readable media.

The instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or individual logic circuits. Therefore, the terms "processor" and "processing circuit" as used herein may represent any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. In addition, in some aspects, the functions described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated into a combined transcoder. Furthermore, the techniques may be implemented entirely in one or more circuits or logic elements.

The techniques of the present disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC), or a set of ICs (e.g., a chipset). Various components, modules, or units are described in the present disclosure to emphasize the functional aspects of a device configured to perform the disclosed techniques, but do not necessarily need to be implemented by different hardware units. Specifically, as described above, the various units may be combined in a transcoder hardware unit, or provided by a collection of interoperable hardware units (including one or more processors as described above) in conjunction with appropriate software and/or firmware.

Various examples have been described. These and other examples are within the scope of the appended claims.

100: Video encoding and decoding system 102: Source device 104: Video source 106: Memory 108: Output interface 110: Computer-readable media 112: Storage device 114: File server 116: Destination device 118: Display device 120: Memory 122: Input interface 130: Quad-tree binary tree (QTBT) structure 132: Coding tree unit (CTU) 200: Video encoder 202: Mode selection unit 204: Error generation Unit 205: ACT unit 206: Transform processing unit 208: Quantization unit 210: Inverse quantization unit 212: Inverse transform processing unit 213: Inverse ACT unit 214: Reconstruction unit 216: Filter unit 218: Decoded picture buffer (DPB) 220: Entropy coding unit 222: Motion estimation unit 224: Motion compensation unit 226: Intra-frame prediction unit 230: Video data memory 300: Video decoder 302: Entropy decoding unit 304: Prediction processing unit 306: Inverse quantization unit 308: Inverse transform processing unit 309: Inverse ACT unit 310: Reconstruction unit 312: Filter unit 314: Decoded picture buffer (DPB) 316: Motion compensation unit 318: Intra-frame prediction unit 320: Coding picture buffer (CPB) memory 350: Process 352: Process 354: Process 356: Process 358: Process 360: Process 370: Process 372: Process 374: Process 376: Process 378: Process 380: Process 400: Process 402: Process 404: Process 406: Process 408: Process 410: Process 412: Process 414: Process 416: Process 418: Process 420: Process 422: Process 424: Process 426: Process 428: Process 430: Process 432: Process 434: Process 436: Process 438: Process 440: Process

FIG. 1 is a block diagram illustrating an example video encoding and decoding system in which the techniques of the present disclosure may be implemented.

2A and 2B are conceptual diagrams illustrating an example quad-tree binary tree (QTBT) structure and a corresponding coding tree unit (CTU).

FIG. 3 is a block diagram illustrating an example video encoder that may implement the techniques of the present disclosure.

FIG. 4 is a block diagram illustrating an example video decoder that may implement the techniques of the present disclosure.

FIG. 5 is a flow chart showing a process for encoding video data.

FIG. 6 is a flow chart showing a process for decoding video data.

FIG. 7 is a flow chart showing a process for decoding video data.

FIG. 8 is a flow chart showing a process for encoding video data.

Domestic storage information (please note in the order of storage institution, date, and number) None Foreign storage information (please note in the order of storage country, institution, date, and number) None

400:Process

402: Process

404: Process

406: Process

408:Process

410: Process

412: Process

414: Process

416: Process

418: Process

Claims (29)

A method for decoding video data, the method comprising the steps of: determining that a block of the video data is encoded using an adaptive color transform (ACT); determining that the block is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for a first chroma component of the block and a second chroma component of the block; determining a first chroma residue block for the first chroma component, wherein the value of the first chroma residue block is equal to the value of the single chroma residue block; determining a symbol value for a second chroma residue block for the second chroma component, wherein the symbol value is equal to one of 1 or -1; determining the second chroma residue block, wherein the value of the second chroma residue block is equal to the symbol value multiplied by the values of the single chroma residue block; determining a quantization parameter (QP) in a second color space for the block based on a slice header QP offset and a picture level QP offset; determining an ACT for the block QP offset, determining the ACT QP offset for the block includes the following steps: determining the ACT QP offset as an ACT QP offset in an ACT QP offset set, wherein the ACT QP offset set includes an ACT QP offset for a luma residue component of the video data, an ACT QP offset for a first chroma residue component of the video data, an ACT QP offset for a second chroma residue component of the video data, and an ACT QP offset for a jointly coded chroma residue component and a sign value of -1, wherein the ACT QP offset for the jointly coded residue component is different from at least one of the ACT QP offset for the first chroma residue component of the video data or the ACT QP offset for the second chroma residue component of the video data, wherein determining the ACT QP offset The QP offset includes the steps of: in response to the block being encoded using the ACT and encoded in the joint chroma mode, determining the ACT QP offset as the ACT QP offset for the jointly coded chroma residue component, wherein the ACT QP offset is determined separately from the slice header QP offset and the picture level QP offset; determining an ACT QP for a first color space for the block based on the QP and the determined ACT QP offset, wherein the first color space is different from the second color space; determining an ACT QP for the block based on the ACT QP to determine the single chroma residue block; determine a first chroma residue block for the first chroma component according to the single chroma residue block, wherein the first chroma residue block is in the first color space; determine a second chroma residue block for the second chroma component according to the single chroma residue block, wherein the second chroma residue block is in the first color space; perform an inverse ACT on the first chroma residue block to convert the first chroma residue block to the second color space; and perform the inverse ACT on the second chroma residue block to convert the second chroma residue block to the second color space. The method of claim 1, wherein determining the ACT QP offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode comprises the steps of: determining the ACT QP offset as a fixed integer value. The method as claimed in claim 1, wherein the first color space comprises a YCgCo color space. The method as described in claim 1 further includes the following steps: adding the converted first chroma residue block to a first predicted chroma block to determine a first reconstructed chroma block; adding the converted second chroma residue block to a second predicted chroma block to determine a second reconstructed chroma block; and outputting the first reconstructed chroma block and the second reconstructed chroma block. The method of claim 1 further comprises the steps of: determining that a second block of the video data is encoded using the ACT; determining that the second block is not encoded in the joint chroma mode; determining a QP for the second block; determining a second ACT QP offset for a first chroma component of the second block based on the second block being encoded using the ACT and not encoded in the joint chroma mode, wherein the second ACT QP offset is determined to be the ACT QP offset for the first chroma residual component of the video data; determining a third ACT QP offset for a second chroma component of the second block based on the second block being encoded using the ACT and not encoded in the joint chroma mode, wherein the third ACT QP offset is determined to be the ACT QP offset for the second chroma residual component of the video data QP offsets, wherein at least one of the second ACT QP offset and the third ACT QP offset is different from the first ACT QP offset. The method of claim 1, wherein determining the first chroma residue block for the first chroma component based on the single chroma residue block comprises the following steps: setting the sample value of the first chroma residue block to be equal to the value of the corresponding sample in the single chroma residue block. The method of claim 6, wherein determining the second chroma residue block for the second chroma component based on the single chroma residue block comprises the following steps: setting the sample value of the second chroma residue block to be equal to the value of the corresponding sample in the first chroma residue block. The method of claim 6, wherein determining the second chroma residue block for the second chroma component based on the single chroma residue block comprises the following steps: setting the sample value of the second chroma residue block to be equal to the value of the corresponding sample in the first chroma residue block multiplied by negative one. The method of claim 1, wherein determining the single chroma residue block based on the ACT QP for the block comprises the following steps: receiving a set of transform coefficients; performing an inverse quantization operation on the set of transform coefficients to determine a set of inverse quantized transform coefficients, wherein an amount of inverse quantization used in the inverse quantization operation is controlled by the ACT QP; and inverse transforming the inverse quantized set of transform coefficients to determine the single chroma residue block. A method for encoding video data, the method comprising the steps of: determining a first chroma residue block for a first chroma component of a block of video data; determining a second chroma residue block for a second chroma component of the block of video data, wherein the first chroma residue block and the second chroma residue block are in a first color space; determining the first chroma residue block of the video data; determining the second ... The block is encoded using an adaptive color transform (ACT); performing the ACT on the first chroma residue block to convert the first chroma residue block to a second color space; performing the ACT on the second chroma residue block to convert the second chroma residue block to the second color space; determining that the block of the video data is encoded in a joint chroma mode , wherein for the joint chroma mode, a single chroma residue block is encoded for the first chroma component of the block and the second chroma component of the block; Determine the single chroma residue block based on the converted first chroma residue block and the converted second chroma residue block; Determine a sign value for a second chroma residue block for the second chroma component, wherein the The symbol value is equal to one of 1 or -1, and the value of the second chroma residue block is equal to the symbol value multiplied by the values of the single chroma residue block; determining a quantization parameter (QP) for the first color space of the block; using all slice header QP offsets and a picture level QP offset to signal the QP parameter; determining an ACT for the second color space of the block QP offset, determining the ACT QP offset for the second color space of the block includes the following steps: determining the ACT QP offset as an ACT QP offset in an ACT QP offset set, wherein the ACT QP offset set includes an ACT QP offset for a luma residue component of the video data, an ACT QP offset for a first chroma residue component of the video data, an ACT QP offset for a second chroma residue component of the video data, and an ACT QP offset for a jointly coded chroma residue component and a sign value of -1, wherein the ACT QP offset for the jointly coded residue component is different from at least one of the ACT QP offset for the first chroma residue component of the video data or the ACT QP offset for the second chroma residue component of the video data, wherein determining the ACT QP offset is an ACT QP offset in an ACT QP offset set, wherein ... The QP offset includes the following steps: in response to the block being encoded using the ACT and being encoded in the joint chroma mode, determining the ACT QP offset as the ACT QP offset for the jointly coded chroma residue component, wherein the ACT QP offset is determined separately from the slice header QP offset and the picture level QP offset; determining an ACT QP for the block based on the QP and the determined ACT QP offset; and quantizing the single chroma residue block based on the ACT QP for the block. The method of claim 10, wherein determining the ACT QP offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode comprises the steps of: determining the ACT QP offset as a fixed integer value. The method as claimed in claim 10, wherein the second color space comprises a YCgCo color space. A device for decoding video data, the device comprising: a memory configured to store video data; one or more processors, the one or more processors implemented in circuits and configured to: determine that a block of the video data is encoded using an adaptive color transform (ACT); determine that the block is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for a first chroma component of the block and a second chroma component of the block; determine a chroma residue block for the first chroma component; A first chroma residue block, wherein the value of the first chroma residue block is equal to the value of the single chroma residue block; determining a symbol value for a second chroma residue block for the second chroma component, wherein the symbol value is equal to one of 1 or -1; determining the second chroma residue block, wherein the value of the second chroma residue block is equal to the symbol value multiplied by the values of the single chroma residue block; determining a quantization parameter (QP) in a second color space for the block based on a slice header QP offset and a picture level QP offset; applying an ACT The QP offset is determined to be an ACT QP offset in an ACT QP offset set, wherein the ACT QP offset set includes an ACT QP offset for a luma residue component of the video data, an ACT QP offset for a first chroma residue component of the video data, an ACT QP offset for a second chroma residue component of the video data, and an ACT QP offset for a jointly coded chroma residue component, and a sign value of -1, wherein the ACT QP offset for the jointly coded residue component is different from at least one of the ACT QP offset for the first chroma residue component of the video data or the ACT QP offset for the second chroma residue component of the video data, wherein to determine the ACT QP offset, The one or more processors are further configured to: in response to the block being encoded using the ACT and encoded in the joint chroma mode, determine the ACT QP offset as the ACT QP offset for the jointly coded chroma residue component, wherein the ACT QP offset is determined separately from the slice header QP offset and the picture level QP offset; determine an ACT QP for a first color space for the block based on the QP and the determined ACT QP offset, wherein the first color space is different from the second color space; determine an ACT QP for the block based on the ACT QP to determine the single chroma residue block; determine a first chroma residue block for the first chroma component according to the single chroma residue block, wherein the first chroma residue block is in the first color space; determine a second chroma residue block for the second chroma component according to the single chroma residue block, wherein the second chroma residue block is in the first color space; perform an inverse ACT on the first chroma residue block to convert the first chroma residue block to the second color space; and perform the inverse ACT on the second chroma residue block to convert the second chroma residue block to the second color space. The apparatus of claim 13, wherein to determine the ACT QP offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode, the one or more processors are further configured to: determine the ACT QP offset as a fixed integer value. The device as claimed in claim 13, wherein the first color space comprises a YCgCo color space. The device of claim 13, wherein the one or more processors are further configured to: add the converted first chroma residue block to a first predicted chroma block to determine a first reconstructed chroma block; add the converted second chroma residue block to a second predicted chroma block to determine a second reconstructed chroma block; and output the first reconstructed chroma block and the second reconstructed chroma block. The apparatus of claim 13, wherein the one or more processors are further configured to: determine that a second block of the video data is encoded using the ACT; determine that the second block is not encoded in the joint chroma mode; determine a QP for the second block; determine a second ACT QP offset for a first chroma component of the second block based on the second block being encoded using the ACT and not encoded in the joint chroma mode, wherein the second ACT QP offset is determined to be the ACT QP offset for the first chroma residual component of the video data; determine a third ACT QP offset for a second chroma component of the second block based on the second block being encoded using the ACT and not encoded in the joint chroma mode, wherein the third ACT The QP offset is determined to be the ACT QP offset of the second chroma residue component of the video data, wherein at least one of the second ACT QP offset and the third ACT QP offset is different from the first ACT QP offset. The device of claim 13, wherein in order to determine the first chroma residue block for the first chroma component based on the single chroma residue block, the one or more processors are further configured to: set the sample value of the first chroma residue block to be equal to the value of the corresponding sample in the single chroma residue block. The device of claim 18, wherein in order to determine the second chroma residue block for the second chroma component based on the single chroma residue block, the one or more processors are further configured to: set the sample value of the second chroma residue block to be equal to the value of the corresponding sample in the first chroma residue block. The device of claim 18, wherein in order to determine the second chroma residue block for the second chroma component based on the single chroma residue block, the one or more processors are further configured to: set the sample value of the second chroma residue block to be equal to the value of the corresponding sample in the first chroma residue block multiplied by negative one. The apparatus of claim 13, wherein to determine the single chroma residue block based on the ACT QP for the block, the one or more processors are further configured to: receive a set of transform coefficients; perform an inverse quantization operation on the set of transform coefficients to determine a set of inverse quantized transform coefficients, wherein an amount of inverse quantization used for the inverse quantization operation is controlled by the ACT QP; and inverse transform the set of inverse quantized transform coefficients to determine the single chroma residue block. The device of claim 13, wherein the device comprises a wireless communication device, the wireless communication device further comprising a receiver configured to receive encoded video data. The device of claim 22, wherein the wireless communication device comprises a telephone handset, and wherein the receiver is configured to demodulate a signal comprising the encoded video data according to a wireless communication standard. The device as described in claim 13 further includes: a display configured to display the decoded video data. The device as claimed in claim 13, wherein the device comprises one or more of the following: a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box. A device for encoding video data, the device comprising: a memory configured to store video data; one or more processors, the one or more processors being implemented in a circuit and configured to: determine a first chroma residue block for a first chroma component of a block of video data; determine a second chroma residue block for a second chroma component of the block of video data, wherein the first chroma The method comprises: determining that the block of video data is encoded using an adaptive color transform (ACT) for encoding the first chroma residue block and the second chroma residue block in a first color space; performing the ACT on the first chroma residue block to convert the first chroma residue block to a second color space; performing the ACT on the second chroma residue block to convert the second chroma residue block to the second color space; and determining that the block of video data is encoded using an adaptive color transform (ACT). The method comprises: determining that the block of the video data is encoded in a joint chroma mode, wherein for the joint chroma mode, a single chroma residue block is encoded for the first chroma component of the block and the second chroma component of the block; determining the single chroma residue block based on the converted first chroma residue block and the converted second chroma residue block; determining a second chroma residue block for the second chroma component; a symbol value for the block, wherein the symbol value is equal to one of 1 or -1, and the value of the second chroma residue block is equal to the symbol value multiplied by the values of the single chroma residue block; determining a quantization parameter (QP) for the first color space of the block; signaling the QP parameter using a slice header QP offset and a picture level QP offset; and quantizing the second color space of the block by a quantization parameter (QP). The QP offset is determined to be an ACT QP offset in an ACT QP offset set, wherein the ACT QP offset set includes an ACT QP offset for a luma residue component of the video data, an ACT QP offset for a first chroma residue component of the video data, an ACT QP offset for a second chroma residue component of the video data, and an ACT QP offset for a jointly coded chroma residue component, and a sign value of -1, wherein the ACT QP offset for the jointly coded residue component is different from at least one of the ACT QP offset for the first chroma residue component of the video data or the ACT QP offset for the second chroma residue component of the video data, wherein to determine the ACT QP offset, the ACT QP offset is determined to be an ACT QP offset in an ACT QP offset set, wherein the ACT QP offset is determined to be an ACT QP offset in an ACT QP offset for a luma residue component of the video data, an ACT QP offset for a second chroma residue component of the video data, and a sign value of -1, wherein the ACT QP offset for the jointly coded residue component is different from at least one of the ACT QP offset for the first chroma residue component of the video data or the ACT QP offset for the second chroma residue component of the video data, wherein to determine the ACT QP offset, the one or more processors are further configured to: in response to the block being encoded using the ACT and encoded in the joint chroma mode, determine the ACT QP offset as the ACT QP offset for the jointly coded chroma residue component, wherein the ACT QP offset is determined separately from the slice header QP offset and the picture level QP offset; determine an ACT QP for the block based on the QP and the ACT QP offset; and quantize the single chroma residue block based on the ACT QP for the block. The apparatus of claim 26, wherein to determine the ACT QP offset for the block based on the block being encoded using the ACT and encoded in the joint chroma mode, the one or more processors are further configured to: determine the ACT QP offset as a fixed integer value. The device as claimed in claim 26, wherein the second color space comprises a YCgCo color space. The device as claimed in claim 26, wherein the device comprises: a camera configured to capture the video data.

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